path: root/doc/autoconf.info

This is autoconf.info, produced by makeinfo version 6.7 from
autoconf.texi.

INFO-DIR-SECTION GNU admin
START-INFO-DIR-ENTRY
* Autoconf: (autoconf).         Create source code configuration scripts
END-INFO-DIR-ENTRY

INFO-DIR-SECTION Individual utilities
START-INFO-DIR-ENTRY
* autoscan: (autoconf)autoscan Invocation.
                                Semi-automatic 'configure.ac' writing
* ifnames: (autoconf)ifnames Invocation.
                                Listing the conditionals in source code
* autoconf: (autoconf)autoconf Invocation.
                                How to create configuration scripts
* autoreconf: (autoconf)autoreconf Invocation.
                                Remaking multiple 'configure' scripts
* configure: (autoconf)configure Invocation.
                                Configuring a package
* config.status: (autoconf)config.status Invocation.
                                Recreating a configuration
END-INFO-DIR-ENTRY

Autoconf: Creating Automatic Configuration Scripts, by David MacKenzie.

   This file documents the GNU Autoconf package for creating scripts to
configure source code packages using templates and an 'm4' macro
package.

   Copyright 2003-2022,2023	Thomas E. Dickey
Copyright 1992, 1993, 1994, 1995, 1996, 1998, 1999, 2000, 2001 Free
Software Foundation, Inc.

   Permission is granted to make and distribute verbatim copies of this
manual provided the copyright notice and this permission notice are
preserved on all copies.

   Permission is granted to copy and distribute modified versions of
this manual under the conditions for verbatim copying, provided that the
entire resulting derived work is distributed under the terms of a
permission notice identical to this one.

   Permission is granted to copy and distribute translations of this
manual into another language, under the above conditions for modified
versions, except that this permission notice may be stated in a
translation approved by the Foundation.


File: autoconf.info,  Node: Top,  Next: Introduction,  Prev: (dir),  Up: (dir)

This file documents the GNU Autoconf package for creating scripts to
configure source code packages using templates and the GNU M4 macro
package.  This is edition 2.52.20240618, for Autoconf version
2.52.20240618.

* Menu:

* Introduction::                Autoconf's purpose, strengths, and weaknesses
* The GNU build system::        A set of tools for portable software packages
* Making configure Scripts::    How to organize and produce Autoconf scripts
* Setup::                       Initialization and output
* Existing Tests::              Macros that check for particular features
* Writing Tests::               How to write new feature checks
* Results::                     What to do with results from feature checks
* Programming in M4::           Layers on top of which Autoconf is written
* Writing Autoconf Macros::     Adding new macros to Autoconf
* Portable Shell::              Shell script portability pitfalls
* Manual Configuration::        Selecting features that can't be guessed
* Site Configuration::          Local defaults for 'configure'
* Running configure scripts::   How to use the Autoconf output
* config.status Invocation::    Recreating a configuration
* Obsolete Constructs::         Kept for backward compatibility
* Questions::                   Questions about Autoconf, with answers
* History::                     History of Autoconf
* Environment Variable Index::  Index of environment variables used
* Output Variable Index::       Index of variables set in output files
* Preprocessor Symbol Index::   Index of C preprocessor symbols defined
* Autoconf Macro Index::        Index of Autoconf macros
* M4 Macro Index::              Index of M4, M4sugar, and M4sh macros
* Concept Index::               General index


The GNU build system

* Automake::                    Escaping Makefile hell
* Libtool::                     Building libraries portably
* Pointers::                    More info on the GNU build system

Making 'configure' Scripts

* Writing configure.ac::        What to put in an Autoconf input file
* autoscan Invocation::         Semi-automatic 'configure.ac' writing
* ifnames Invocation::          Listing the conditionals in source code
* autoconf Invocation::         How to create configuration scripts
* autoreconf Invocation::       Remaking multiple 'configure' scripts

Writing 'configure.ac'

* Shell Script Compiler::       Autoconf as solution of a problem
* Autoconf Language::           Programming in Autoconf
* configure.ac Layout::         Standard organization of configure.ac

Initialization and Output Files

* Notices::                     Copyright, version numbers in 'configure'
* Input::                       Where Autoconf should find files
* Output::                      Outputting results from the configuration
* Configuration Actions::       Preparing the output based on results
* Configuration Files::         Creating output files
* Makefile Substitutions::      Using output variables in 'Makefile's
* Configuration Headers::       Creating a configuration header file
* Configuration Commands::      Running arbitrary instantiation commands
* Configuration Links::         Links depending from the configuration
* Subdirectories::              Configuring independent packages together
* Default Prefix::              Changing the default installation prefix

Substitutions in Makefiles

* Preset Output Variables::     Output variables that are always set
* Installation Directory Variables::  Other preset output variables
* Build Directories::           Supporting multiple concurrent compiles
* Automatic Remaking::          Makefile rules for configuring

Configuration Header Files

* Header Templates::            Input for the configuration headers
* autoheader Invocation::       How to create configuration templates
* Autoheader Macros::           How to specify CPP templates

Existing Tests

* Common Behavior::             Macros' standard schemes
* Alternative Programs::        Selecting between alternative programs
* Files::                       Checking for the existence of files
* Libraries::                   Library archives that might be missing
* Library Functions::           C library functions that might be missing
* Header Files::                Header files that might be missing
* Declarations::                Declarations that may be missing
* Structures::                  Structures or members that might be missing
* Types::                       Types that might be missing
* Compilers and Preprocessors::  Checking for compiling programs
* System Services::             Operating system services
* UNIX Variants::               Special kludges for specific UNIX variants

Common Behavior

* Standard Symbols::            Symbols defined by the macros
* Default Includes::            Includes used by the generic macros

Alternative Programs

* Particular Programs::         Special handling to find certain programs
* Generic Programs::            How to find other programs

Library Functions

* Function Portability::        Pitfalls with usual functions
* Particular Functions::        Special handling to find certain functions
* Generic Functions::           How to find other functions

Header Files

* Particular Headers::          Special handling to find certain headers
* Generic Headers::             How to find other headers

Declarations

* Particular Declarations::     Macros to check for certain declarations
* Generic Declarations::        How to find other declarations

Structures

* Particular Structures::       Macros to check for certain structure members
* Generic Structures::          How to find other structure members

Types

* Particular Types::            Special handling to find certain types
* Generic Types::               How to find other types

Compilers and Preprocessors

* Generic Compiler Characteristics::  Language independent tests
* C Compiler::                  Checking its characteristics
* C++ Compiler::                Likewise
* Fortran 77 Compiler::         Likewise

Writing Tests

* Examining Declarations::      Detecting header files and declarations
* Examining Syntax::            Detecting language syntax features
* Examining Libraries::         Detecting functions and global variables
* Run Time::                    Testing for run-time features
* Systemology::                 A zoology of operating systems
* Multiple Cases::              Tests for several possible values
* Language Choice::             Selecting which language to use for testing

Checking Run Time Behavior

* Test Programs::               Running test programs
* Guidelines::                  General rules for writing test programs
* Test Functions::              Avoiding pitfalls in test programs

Results of Tests

* Defining Symbols::            Defining C preprocessor symbols
* Setting Output Variables::    Replacing variables in output files
* Caching Results::             Speeding up subsequent 'configure' runs
* Printing Messages::           Notifying 'configure' users

Caching Results

* Cache Variable Names::        Shell variables used in caches
* Cache Files::                 Files 'configure' uses for caching
* Cache Checkpointing::         Loading and saving the cache file

Programming in M4

* M4 Quotation::                Protecting macros from unwanted expansion
* Programming in M4sugar::      Convenient pure M4 macros

M4 Quotation

* Active Characters::           Characters that change the behavior of m4
* One Macro Call::              Quotation and one macro call
* Quotation and Nested Macros::  Macros calling macros
* Quadrigraphs::                Another way to escape special characters
* Quotation Rule Of Thumb::     One parenthesis, one quote

Programming in M4sugar

* Redefined M4 Macros::         M4 builtins changed in M4sugar
* Forbidden Patterns::          Catching unexpanded macros

Writing Autoconf Macros

* Macro Definitions::           Basic format of an Autoconf macro
* Macro Names::                 What to call your new macros
* Reporting Messages::          Notifying 'autoconf' users
* Dependencies Between Macros::  What to do when macros depend on other macros
* Obsoleting Macros::           Warning about old ways of doing things
* Coding Style::                Writing Autoconf macros à la Autoconf

Dependencies Between Macros

* Prerequisite Macros::         Ensuring required information
* Suggested Ordering::          Warning about possible ordering problems

Portable Shell Programming

* Shellology::                  A zoology of shells
* Here-Documents::              Quirks and tricks
* File Descriptors::            FDs and redirections
* File System Conventions::     File- and pathnames
* Shell Substitutions::         Variable and command expansions
* Assignments::                 Varying side effects of assignments
* Special Shell Variables::     Variables you should not change
* Limitations of Builtins::     Portable use of not so portable /bin/sh
* Limitations of Usual Tools::  Portable use of portable tools
* Limitations of Make::         Portable Makefiles

Manual Configuration

* Specifying Names::            Specifying the system type
* Canonicalizing::              Getting the canonical system type
* Using System Type::           What to do with the system type

Site Configuration

* External Software::           Working with other optional software
* Package Options::             Selecting optional features
* Pretty Help Strings::         Formatting help string
* Site Details::                Configuring site details
* Transforming Names::          Changing program names when installing
* Site Defaults::               Giving 'configure' local defaults

Transforming Program Names When Installing

* Transformation Options::      'configure' options to transform names
* Transformation Examples::     Sample uses of transforming names
* Transformation Rules::        'Makefile' uses of transforming names

Running 'configure' Scripts

* Basic Installation::          Instructions for typical cases
* Compilers and Options::       Selecting compilers and optimization
* Multiple Architectures::      Compiling for multiple architectures at once
* Installation Names::          Installing in different directories
* Optional Features::           Selecting optional features
* System Type::                 Specifying the system type
* Sharing Defaults::            Setting site-wide defaults for 'configure'
* Environment Variables::       Defining environment variables.
* configure Invocation::        Changing how 'configure' runs

Obsolete Constructs

* Obsolete config.status Use::  Different calling convention
* acconfig.h::                  Additional entries in 'config.h.in'
* autoupdate Invocation::       Automatic update of 'configure.ac'
* Obsolete Macros::             Backward compatibility macros
* Autoconf 1::                  Tips for upgrading your files
* Autoconf 2.13::               Some fresher tips

Upgrading From Version 1

* Changed File Names::          Files you might rename
* Changed Makefiles::           New things to put in 'Makefile.in'
* Changed Macros::              Macro calls you might replace
* Changed Results::             Changes in how to check test results
* Changed Macro Writing::       Better ways to write your own macros

Upgrading From Version 2.13

* Changed Quotation::           Broken code which used to work
* New Macros::                  Interaction with foreign macros

Questions About Autoconf

* Distributing::                Distributing 'configure' scripts
* Why GNU m4::                  Why not use the standard M4?
* Bootstrapping::               Autoconf and GNU M4 require each other?
* Why Not Imake::               Why GNU uses 'configure' instead of Imake

History of Autoconf

* Genesis::                     Prehistory and naming of 'configure'
* Exodus::                      The plagues of M4 and Perl
* Leviticus::                   The priestly code of portability arrives
* Numbers::                     Growth and contributors
* Deuteronomy::                 Approaching the promises of easy configuration



File: autoconf.info,  Node: Introduction,  Next: The GNU build system,  Prev: Top,  Up: Top

1 Introduction
**************

 A physicist, an engineer, and a computer scientist were discussing the
     nature of God.  "Surely a Physicist," said the physicist, "because
         early in the Creation, God made Light; and you know, Maxwell's
  equations, the dual nature of electromagnetic waves, the relativistic
           consequences..." "An Engineer!," said the engineer, "because
before making Light, God split the Chaos into Land and Water; it takes a
      hell of an engineer to handle that big amount of mud, and orderly
           separation of solids from liquids..." The computer scientist
  shouted: "And the Chaos, where do you think it was coming from, hmm?"

                                                            --Anonymous

   Autoconf is a tool for producing shell scripts that automatically
configure software source code packages to adapt to many kinds of
UNIX-like systems.  The configuration scripts produced by Autoconf are
independent of Autoconf when they are run, so their users do not need to
have Autoconf.

   The configuration scripts produced by Autoconf require no manual user
intervention when run; they do not normally even need an argument
specifying the system type.  Instead, they individually test for the
presence of each feature that the software package they are for might
need.  (Before each check, they print a one-line message stating what
they are checking for, so the user doesn't get too bored while waiting
for the script to finish.)  As a result, they deal well with systems
that are hybrids or customized from the more common UNIX variants.
There is no need to maintain files that list the features supported by
each release of each variant of UNIX.

   For each software package that Autoconf is used with, it creates a
configuration script from a template file that lists the system features
that the package needs or can use.  After the shell code to recognize
and respond to a system feature has been written, Autoconf allows it to
be shared by many software packages that can use (or need) that feature.
If it later turns out that the shell code needs adjustment for some
reason, it needs to be changed in only one place; all of the
configuration scripts can be regenerated automatically to take advantage
of the updated code.

   The Metaconfig package is similar in purpose to Autoconf, but the
scripts it produces require manual user intervention, which is quite
inconvenient when configuring large source trees.  Unlike Metaconfig
scripts, Autoconf scripts can support cross-compiling, if some care is
taken in writing them.

   Autoconf does not solve all problems related to making portable
software packages--for a more complete solution, it should be used in
concert with other GNU build tools like Automake and Libtool.  These
other tools take on jobs like the creation of a portable, recursive
'Makefile' with all of the standard targets, linking of shared
libraries, and so on.  *Note The GNU build system::, for more
information.

   Autoconf imposes some restrictions on the names of macros used with
'#if' in C programs (*note Preprocessor Symbol Index::).

   Autoconf requires GNU M4 in order to generate the scripts.  It uses
features that some UNIX versions of M4, including GNU M4 1.3, do not
have.  You must use version 1.4 or later of GNU M4.

   *Note Autoconf 1::, for information about upgrading from version 1.
*Note History::, for the story of Autoconf's development.  *Note
Questions::, for answers to some common questions about Autoconf.

   See the Autoconf web page(1) for up-to-date information, details on
the mailing lists, pointers to a list of known bugs, etc.

   Mail suggestions to the Autoconf mailing list <autoconf@gnu.org>.

   Bug reports should be preferably submitted to the Autoconf Gnats
database(2), or sent to the Autoconf Bugs mailing list
<bug-autoconf@gnu.org>.  If possible, first check that your bug is not
already solved in current development versions, and that it has not been
reported yet.  Be sure to include all the needed information and a short
'configure.ac' that demonstrates the problem.

   Autoconf's development tree is accessible via CVS; see the Autoconf
web page for details.  There is also a CVSweb interface to the Autoconf
development tree(3).  Patches relative to the current CVS version can be
sent for review to the Autoconf Patches mailing list
<autoconf-patches@gnu.org>.

   Because of its mission, Autoconf includes only a set of often-used
macros that have already demonstrated their usefulness.  Nevertheless,
if you wish to share your macros, or find existing ones, see the
Autoconf Macro Archive(4), which is kindly run by Peter Simons
<simons@computer.org>.

   ---------- Footnotes ----------

   (1) Autoconf web page,
<http://www.gnu.org/software/autoconf/autoconf.html>.

   (2) Autoconf Gnats database,
<http://sources.redhat.com/cgi-bin/gnatsweb.pl?database=autoconf>.

   (3) CVSweb interface to the Autoconf development tree,
<http://subversions.gnu.org/cgi-bin/cvsweb/autoconf/>.

   (4) Autoconf Macro Archive,
<http://www.gnu.org/software/ac-archive/>.


File: autoconf.info,  Node: The GNU build system,  Next: Making configure Scripts,  Prev: Introduction,  Up: Top

2 The GNU build system
**********************

Autoconf solves an important problem--reliable discovery of
system-specific build and runtime information--but this is only one
piece of the puzzle for the development of portable software.  To this
end, the GNU project has developed a suite of integrated utilities to
finish the job Autoconf started: the GNU build system, whose most
important components are Autoconf, Automake, and Libtool.  In this
chapter, we introduce you to those tools, point you to sources of more
information, and try to convince you to use the entire GNU build system
for your software.

* Menu:

* Automake::                    Escaping Makefile hell
* Libtool::                     Building libraries portably
* Pointers::                    More info on the GNU build system


File: autoconf.info,  Node: Automake,  Next: Libtool,  Prev: The GNU build system,  Up: The GNU build system

2.1 Automake
============

The ubiquity of 'make' means that a 'Makefile' is almost the only viable
way to distribute automatic build rules for software, but one quickly
runs into 'make''s numerous limitations.  Its lack of support for
automatic dependency tracking, recursive builds in subdirectories,
reliable timestamps (e.g.  for network filesystems), and so on, mean
that developers must painfully (and often incorrectly) reinvent the
wheel for each project.  Portability is non-trivial, thanks to the
quirks of 'make' on many systems.  On top of all this is the manual
labor required to implement the many standard targets that users have
come to expect ('make install', 'make distclean', 'make uninstall',
etc.).  Since you are, of course, using Autoconf, you also have to
insert repetitive code in your 'Makefile.in' to recognize '@CC@',
'@CFLAGS@', and other substitutions provided by 'configure'.  Into this
mess steps "Automake".

   Automake allows you to specify your build needs in a 'Makefile.am'
file with a vastly simpler and more powerful syntax than that of a plain
'Makefile', and then generates a portable 'Makefile.in' for use with
Autoconf.  For example, the 'Makefile.am' to build and install a simple
"Hello world" program might look like:

     bin_PROGRAMS = hello
     hello_SOURCES = hello.c

The resulting 'Makefile.in' (~400 lines) automatically supports all the
standard targets, the substitutions provided by Autoconf, automatic
dependency tracking, 'VPATH' building, and so on.  'make' will build the
'hello' program, and 'make install' will install it in '/usr/local/bin'
(or whatever prefix was given to 'configure', if not '/usr/local').

   Automake may require that additional tools be present on the
_developer's_ machine.  For example, the 'Makefile.in' that the
developer works with may not be portable (e.g.  it might use special
features of your compiler to automatically generate dependency
information).  Running 'make dist', however, produces a
'hello-1.0.tar.gz' package (or whatever the program/version is) with a
'Makefile.in' that will work on any system.

   The benefits of Automake increase for larger packages (especially
ones with subdirectories), but even for small programs the added
convenience and portability can be substantial.  And that's not all...


File: autoconf.info,  Node: Libtool,  Next: Pointers,  Prev: Automake,  Up: The GNU build system

2.2 Libtool
===========

Very often, one wants to build not only programs, but libraries, so that
other programs can benefit from the fruits of your labor.  Ideally, one
would like to produce _shared_ (dynamically-linked) libraries, which can
be used by multiple programs without duplication on disk or in memory
and can be updated independently of the linked programs.  Producing
shared libraries portably, however, is the stuff of nightmares--each
system has its own incompatible tools, compiler flags, and magic
incantations.  Fortunately, GNU provides a solution: "Libtool".

   Libtool handles all the requirements of building shared libraries for
you, and at this time seems to be the _only_ way to do so with any
portability.  It also handles many other headaches, such as: the
interaction of 'Makefile' rules with the variable suffixes of shared
libraries, linking reliably to shared libraries before they are
installed by the superuser, and supplying a consistent versioning system
(so that different versions of a library can be installed or upgraded
without breaking binary compatibility).  Although Libtool, like
Autoconf, can be used on its own, it is most simply utilized in
conjunction with Automake--there, Libtool is used automatically whenever
shared libraries are needed, and you need not know its syntax.


File: autoconf.info,  Node: Pointers,  Prev: Libtool,  Up: The GNU build system

2.3 Pointers
============

Developers who are used to the simplicity of 'make' for small projects
on a single system might be daunted at the prospect of learning to use
Automake and Autoconf.  As your software is distributed to more and more
users, however, you will otherwise quickly find yourself putting lots of
effort into reinventing the services that the GNU build tools provide,
and making the same mistakes that they once made and overcame.
(Besides, since you're already learning Autoconf, Automake will be a
piece of cake.)

   There are a number of places that you can go to for more information
on the GNU build tools.

   - Web

     The home pages for Autoconf(1), and Libtool(2).

   - Books

     The book 'GNU Autoconf, Automake and Libtool'(3) describes the
     complete GNU build environment.  You can also find the entire book
     on-line at "The Goat Book" home page(4).

   - Tutorials and Examples

     The Autoconf Developer Page(5) maintains links to a number of
     Autoconf/Automake tutorials online, and also links to the Autoconf
     Macro Archive(6).

   ---------- Footnotes ----------

   (1) Autoconf, <http://www.gnu.org/software/autoconf/>.

   (2) Libtool, <http://www.gnu.org/software/libtool/>.

   (3) 'GNU Autoconf, Automake and Libtool', by G. V. Vaughan, B.
Elliston, T. Tromey, and I. L. Taylor.  New Riders, 2000, ISBN
1578701902.

   (4) "The Goat Book" home page, <http://sources.redhat.com/autobook/>.

   (5) Autoconf Developer Page, <http://sources.redhat.com/autoconf/>.

   (6) Autoconf Macro Archive,
<http://www.gnu.org/software/ac-archive/>.


File: autoconf.info,  Node: Making configure Scripts,  Next: Setup,  Prev: The GNU build system,  Up: Top

3 Making 'configure' Scripts
****************************

The configuration scripts that Autoconf produces are by convention
called 'configure'.  When run, 'configure' creates several files,
replacing configuration parameters in them with appropriate values.  The
files that 'configure' creates are:

   - one or more 'Makefile' files, one in each subdirectory of the
     package (*note Makefile Substitutions::);

   - optionally, a C header file, the name of which is configurable,
     containing '#define' directives (*note Configuration Headers::);

   - a shell script called 'config.status' that, when run, will recreate
     the files listed above (*note config.status Invocation::);

   - an optional shell script normally called 'config.cache' (created
     when using 'configure --config-cache') that saves the results of
     running many of the tests (*note Cache Files::);

   - a file called 'config.log' containing any messages produced by
     compilers, to help debugging if 'configure' makes a mistake.

   To create a 'configure' script with Autoconf, you need to write an
Autoconf input file 'configure.ac' (or 'configure.in') and run
'autoconf' on it.  If you write your own feature tests to supplement
those that come with Autoconf, you might also write files called
'aclocal.m4' and 'acsite.m4'.  If you use a C header file to contain
'#define' directives, you might also run 'autoheader', and you will
distribute the generated file 'config.h.in' with the package.

   Here is a diagram showing how the files that can be used in
configuration are produced.  Programs that are executed are suffixed by
'*'.  Optional files are enclosed in square brackets ('[]').  'autoconf'
and 'autoheader' also read the installed Autoconf macro files (by
reading 'autoconf.m4').

Files used in preparing a software package for distribution:
     your source files --> [autoscan*] --> [configure.scan] --> configure.ac

     configure.ac --.
                    |   .------> autoconf* -----> configure
     [aclocal.m4] --+---+
                    |   `-----> [autoheader*] --> [config.h.in]
     [acsite.m4] ---'

     Makefile.in -------------------------------> Makefile.in

Files used in configuring a software package:
                            .-------------> [config.cache]
     configure* ------------+-------------> config.log
                            |
     [config.h.in] -.       v            .-> [config.h] -.
                    +--> config.status* -+               +--> make*
     Makefile.in ---'                    `-> Makefile ---'

* Menu:

* Writing configure.ac::        What to put in an Autoconf input file
* autoscan Invocation::         Semi-automatic 'configure.ac' writing
* ifnames Invocation::          Listing the conditionals in source code
* autoconf Invocation::         How to create configuration scripts
* autoreconf Invocation::       Remaking multiple 'configure' scripts


File: autoconf.info,  Node: Writing configure.ac,  Next: autoscan Invocation,  Prev: Making configure Scripts,  Up: Making configure Scripts

3.1 Writing 'configure.ac'
==========================

To produce a 'configure' script for a software package, create a file
called 'configure.ac' that contains invocations of the Autoconf macros
that test the system features your package needs or can use.  Autoconf
macros already exist to check for many features; see *note Existing
Tests::, for their descriptions.  For most other features, you can use
Autoconf template macros to produce custom checks; see *note Writing
Tests::, for information about them.  For especially tricky or
specialized features, 'configure.ac' might need to contain some
hand-crafted shell commands; see *note Portable Shell::.  The 'autoscan'
program can give you a good start in writing 'configure.ac' (*note
autoscan Invocation::, for more information).

   Previous versions of Autoconf promoted the name 'configure.in', which
is somewhat ambiguous (the tool needed to produce this file is not
described by its extension), and introduces a slight confusion with
'config.h.in' and so on (for which '.in' means "to be processed by
'configure'").  Using 'configure.ac' is now preferred.

* Menu:

* Shell Script Compiler::       Autoconf as solution of a problem
* Autoconf Language::           Programming in Autoconf
* configure.ac Layout::         Standard organization of configure.ac


File: autoconf.info,  Node: Shell Script Compiler,  Next: Autoconf Language,  Prev: Writing configure.ac,  Up: Writing configure.ac

3.1.1 A Shell Script Compiler
-----------------------------

Just as for any other computer language, in order to properly program
'configure.ac' in Autoconf you must understand _what_ problem the
language tries to address and _how_ it does so.

   The problem Autoconf addresses is that the world is a mess.  After
all, you are using Autoconf in order to have your package compile easily
on all sorts of different systems, some of them being extremely hostile.
Autoconf itself bears the price for these differences: 'configure' must
run on all those systems, and thus 'configure' must limit itself to
their lowest common denominator of features.

   Naturally, you might then think of shell scripts; who needs
'autoconf'?  A set of properly written shell functions is enough to make
it easy to write 'configure' scripts by hand.  Sigh!  Unfortunately,
shell functions do not belong to the least common denominator;
therefore, where you would like to define a function and use it ten
times, you would instead need to copy its body ten times.

   So, what is really needed is some kind of compiler, 'autoconf', that
takes an Autoconf program, 'configure.ac', and transforms it into a
portable shell script, 'configure'.

   How does 'autoconf' perform this task?

   There are two obvious possibilities: creating a brand new language or
extending an existing one.  The former option is very attractive: all
sorts of optimizations could easily be implemented in the compiler and
many rigorous checks could be performed on the Autoconf program (e.g.
rejecting any non-portable construct).  Alternatively, you can extend an
existing language, such as the 'sh' (Bourne shell) language.

   Autoconf does the latter: it is a layer on top of 'sh'.  It was
therefore most convenient to implement 'autoconf' as a macro expander: a
program that repeatedly performs "macro expansions" on text input,
replacing macro calls with macro bodies and producing a pure 'sh' script
in the end.  Instead of implementing a dedicated Autoconf macro
expander, it is natural to use an existing general-purpose macro
language, such as M4, and implement the extensions as a set of M4
macros.


File: autoconf.info,  Node: Autoconf Language,  Next: configure.ac Layout,  Prev: Shell Script Compiler,  Up: Writing configure.ac

3.1.2 The Autoconf Language
---------------------------

The Autoconf language is very different from many other computer
languages because it treats actual code the same as plain text.  Whereas
in C, for instance, data and instructions have very different syntactic
status, in Autoconf their status is rigorously the same.  Therefore, we
need a means to distinguish literal strings from text to be expanded:
quotation.

   When calling macros that take arguments, there must not be any blank
space between the macro name and the open parenthesis.  Arguments should
be enclosed within the M4 quote characters '[' and ']', and be separated
by commas.  Any leading spaces in arguments are ignored, unless they are
quoted.  You may safely leave out the quotes when the argument is simple
text, but _always_ quote complex arguments such as other macro calls.
This rule applies recursively for every macro call, including macros
called from other macros.

   For instance:

     AC_CHECK_HEADER([stdio.h],
                     [AC_DEFINE([HAVE_STDIO_H])],
                     [AC_MSG_ERROR([Sorry, can't do anything for you])])

is quoted properly.  You may safely simplify its quotation to:

     AC_CHECK_HEADER(stdio.h,
                     [AC_DEFINE(HAVE_STDIO_H)],
                     [AC_MSG_ERROR([Sorry, can't do anything for you])])

Notice that the argument of 'AC_MSG_ERROR' is still quoted; otherwise,
its comma would have been interpreted as an argument separator.

   The following example is wrong and dangerous, as it is underquoted:

     AC_CHECK_HEADER(stdio.h,
                     AC_DEFINE(HAVE_STDIO_H),
                     AC_MSG_ERROR([Sorry, can't do anything for you]))

   In other cases, you may have to use text that also resembles a macro
call.  You must quote that text even when it is not passed as a macro
argument:

     echo "Hard rock was here!  --[AC_DC]"

which will result in

     echo "Hard rock was here!  --AC_DC"

When you use the same text in a macro argument, you must therefore have
an extra quotation level (since one is stripped away by the macro
substitution).  In general, then, it is a good idea to _use double
quoting for all literal string arguments_:

     AC_MSG_WARN([[AC_DC stinks  --Iron Maiden]])

   You are now able to understand one of the constructs of Autoconf that
has been continually misunderstood... The rule of thumb is that
_whenever you expect macro expansion, expect quote expansion_; i.e.,
expect one level of quotes to be lost.  For instance:

     AC_COMPILE_IFELSE([char b[10];],, [AC_MSG_ERROR([you lose])])

is incorrect: here, the first argument of 'AC_COMPILE_IFELSE' is 'char
b[10];' and will be expanded once, which results in 'char b10;'.  (There
was an idiom common in Autoconf's past to address this issue via the M4
'changequote' primitive, but do not use it!)  Let's take a closer look:
the author meant the first argument to be understood as a literal, and
therefore it must be quoted twice:

     AC_COMPILE_IFELSE([[char b[10];]],, [AC_MSG_ERROR([you lose])])

Voilà, you actually produce 'char b[10];' this time!

   The careful reader will notice that, according to these guidelines,
the "properly" quoted 'AC_CHECK_HEADER' example above is actually
lacking three pairs of quotes!  Nevertheless, for the sake of
readability, double quotation of literals is used only where needed in
this manual.

   Some macros take optional arguments, which this documentation
represents as [ARG] (not to be confused with the quote characters).  You
may just leave them empty, or use '[]' to make the emptiness of the
argument explicit, or you may simply omit the trailing commas.  The
three lines below are equivalent:

     AC_CHECK_HEADERS(stdio.h, [], [], [])
     AC_CHECK_HEADERS(stdio.h,,,)
     AC_CHECK_HEADERS(stdio.h)

   It is best to put each macro call on its own line in 'configure.ac'.
Most of the macros don't add extra newlines; they rely on the newline
after the macro call to terminate the commands.  This approach makes the
generated 'configure' script a little easier to read by not inserting
lots of blank lines.  It is generally safe to set shell variables on the
same line as a macro call, because the shell allows assignments without
intervening newlines.

   You can include comments in 'configure.ac' files by starting them
with the '#'.  For example, it is helpful to begin 'configure.ac' files
with a line like this:

     # Process this file with autoconf to produce a configure script.


File: autoconf.info,  Node: configure.ac Layout,  Prev: Autoconf Language,  Up: Writing configure.ac

3.1.3 Standard 'configure.ac' Layout
------------------------------------

The order in which 'configure.ac' calls the Autoconf macros is not
important, with a few exceptions.  Every 'configure.ac' must contain a
call to 'AC_INIT' before the checks, and a call to 'AC_OUTPUT' at the
end (*note Output::).  Additionally, some macros rely on other macros
having been called first, because they check previously set values of
some variables to decide what to do.  These macros are noted in the
individual descriptions (*note Existing Tests::), and they also warn you
when 'configure' is created if they are called out of order.

   To encourage consistency, here is a suggested order for calling the
Autoconf macros.  Generally speaking, the things near the end of this
list are those that could depend on things earlier in it.  For example,
library functions could be affected by types and libraries.

     Autoconf requirements
     'AC_INIT(PACKAGE, VERSION, BUG-REPORT-ADDRESS)'
     information on the package
     checks for programs
     checks for libraries
     checks for header files
     checks for types
     checks for structures
     checks for compiler characteristics
     checks for library functions
     checks for system services
     'AC_CONFIG_FILES([FILE...])'
     'AC_OUTPUT'


File: autoconf.info,  Node: autoscan Invocation,  Next: ifnames Invocation,  Prev: Writing configure.ac,  Up: Making configure Scripts

3.2 Using 'autoscan' to Create 'configure.ac'
=============================================

The 'autoscan' program can help you create and/or maintain a
'configure.ac' file for a software package.  'autoscan' examines source
files in the directory tree rooted at a directory given as a command
line argument, or the current directory if none is given.  It searches
the source files for common portability problems and creates a file
'configure.scan' which is a preliminary 'configure.ac' for that package,
and checks a possibly existing 'configure.ac' for completeness.

   When using 'autoscan' to create a 'configure.ac', you should manually
examine 'configure.scan' before renaming it to 'configure.ac'; it will
probably need some adjustments.  Occasionally, 'autoscan' outputs a
macro in the wrong order relative to another macro, so that 'autoconf'
produces a warning; you need to move such macros manually.  Also, if you
want the package to use a configuration header file, you must add a call
to 'AC_CONFIG_HEADERS' (*note Configuration Headers::).  You might also
have to change or add some '#if' directives to your program in order to
make it work with Autoconf (*note ifnames Invocation::, for information
about a program that can help with that job).

   When using 'autoscan' to maintain a 'configure.ac', simply consider
adding its suggestions.  The file 'autoscan.log' will contain detailed
information on why a macro is requested.

   'autoscan' uses several data files (installed along with Autoconf) to
determine which macros to output when it finds particular symbols in a
package's source files.  These data files all have the same format: each
line consists of a symbol, whitespace, and the Autoconf macro to output
if that symbol is encountered.  Lines starting with '#' are comments.

   'autoscan' is only installed if you already have Perl installed.
'autoscan' accepts the following options:

'--help'
'-h'
     Print a summary of the command line options and exit.

'--version'
'-V'
     Print the version number of Autoconf and exit.

'--verbose'
'-v'
     Print the names of the files it examines and the potentially
     interesting symbols it finds in them.  This output can be
     voluminous.

'--autoconf-dir=DIR'
'-A DIR'
     Override the location where the installed Autoconf data files are
     looked for.  You can also set the 'AC_MACRODIR' environment
     variable to a directory; this option overrides the environment
     variable.

     This option is rarely needed and dangerous; it is only used when
     one plays with different versions of Autoconf simultaneously.


File: autoconf.info,  Node: ifnames Invocation,  Next: autoconf Invocation,  Prev: autoscan Invocation,  Up: Making configure Scripts

3.3 Using 'ifnames' to List Conditionals
========================================

'ifnames' can help you write 'configure.ac' for a software package.  It
prints the identifiers that the package already uses in C preprocessor
conditionals.  If a package has already been set up to have some
portability, 'ifnames' can thus help you figure out what its 'configure'
needs to check for.  It may help fill in some gaps in a 'configure.ac'
generated by 'autoscan' (*note autoscan Invocation::).

   'ifnames' scans all of the C source files named on the command line
(or the standard input, if none are given) and writes to the standard
output a sorted list of all the identifiers that appear in those files
in '#if', '#elif', '#ifdef', or '#ifndef' directives.  It prints each
identifier on a line, followed by a space-separated list of the files in
which that identifier occurs.

'ifnames' accepts the following options:

'--help'
'-h'
     Print a summary of the command line options and exit.

'--version'
'-V'
     Print the version number of Autoconf and exit.


File: autoconf.info,  Node: autoconf Invocation,  Next: autoreconf Invocation,  Prev: ifnames Invocation,  Up: Making configure Scripts

3.4 Using 'autoconf' to Create 'configure'
==========================================

To create 'configure' from 'configure.ac', run the 'autoconf' program
with no arguments.  'autoconf' processes 'configure.ac' with the 'm4'
macro processor, using the Autoconf macros.  If you give 'autoconf' an
argument, it reads that file instead of 'configure.ac' and writes the
configuration script to the standard output instead of to 'configure'.
If you give 'autoconf' the argument '-', it reads from the standard
input instead of 'configure.ac' and writes the configuration script to
the standard output.

   The Autoconf macros are defined in several files.  Some of the files
are distributed with Autoconf; 'autoconf' reads them first.  Then it
looks for the optional file 'acsite.m4' in the directory that contains
the distributed Autoconf macro files, and for the optional file
'aclocal.m4' in the current directory.  Those files can contain your
site's or the package's own Autoconf macro definitions (*note Writing
Autoconf Macros::, for more information).  If a macro is defined in more
than one of the files that 'autoconf' reads, the last definition it
reads overrides the earlier ones.

   'autoconf' accepts the following options:

'--help'
'-h'
     Print a summary of the command line options and exit.

'--version'
'-V'
     Print the version number of Autoconf and exit.

'--verbose'
'-v'
     Report processing steps.

'--debug'
'-d'
     Don't remove the temporary files.

'--autoconf-dir=DIR'
'-A DIR'
     Override the location where the installed Autoconf data files are
     looked for.  You can also set the 'AC_MACRODIR' environment
     variable to a directory; this option overrides the environment
     variable.

     This option is rarely needed and dangerous; it is only used when
     one plays with different versions of Autoconf simultaneously.

'--localdir=DIR'
'-l DIR'
     Look for the package file 'aclocal.m4' in directory DIR instead of
     in the current directory.

'--output=FILE'
'-o FILE'
     Save output (script or trace) to FILE.  The file '-' stands for the
     standard output.

'--warnings=CATEGORY'
'-W CATEGORY'
     Report the warnings related to CATEGORY (which can actually be a
     comma separated list).  *Note Reporting Messages::, macro
     'AC_DIAGNOSE', for a comprehensive list of categories.  Special
     values include:

     'all'
          report all the warnings

     'none'
          report none

     'error'
          treats warnings as errors

     'no-CATEGORY'
          disable warnings falling into CATEGORY

     Warnings about 'syntax' are enabled by default, and the environment
     variable 'WARNINGS', a comma separated list of categories, is
     honored.  'autoconf -W CATEGORY' will actually behave as if you had
     run:

          autoconf --warnings=syntax,$WARNINGS,CATEGORY

     If you want to disable 'autoconf''s defaults and 'WARNINGS', but
     (for example) enable the warnings about obsolete constructs, you
     would use '-W none,obsolete'.

     'autoconf' displays a back trace for errors, but not for warnings;
     if you want them, just pass '-W error'.  For instance, on this
     'configure.ac':

          AC_DEFUN([INNER],
          [AC_TRY_RUN([true])])

          AC_DEFUN([OUTER],
          [INNER])

          AC_INIT
          OUTER

     you get:

          $ autoconf -Wcross
          configure.ac:8: warning: AC_TRY_RUN called without default \
          to allow cross compiling
          $ autoconf -Wcross,error
          configure.ac:8: error: AC_TRY_RUN called without default \
          to allow cross compiling
          acgeneral.m4:3044: AC_TRY_RUN is expanded from...
          configure.ac:2: INNER is expanded from...
          configure.ac:5: OUTER is expanded from...
          configure.ac:8: the top level

'--trace=MACRO[:FORMAT]'
'-t MACRO[:FORMAT]'
     Do not create the 'configure' script, but list the calls to MACRO
     according to the FORMAT.  Multiple '--trace' arguments can be used
     to list several macros.  Multiple '--trace' arguments for a single
     macro are not cumulative; instead, you should just make FORMAT as
     long as needed.

     The FORMAT is a regular string, with newlines if desired, and
     several special escape codes.  It defaults to '$f:$l:$n:$%'; see
     below for details on the FORMAT.

'--initialization'
'-i'
     By default, '--trace' does not trace the initialization of the
     Autoconf macros (typically the 'AC_DEFUN' definitions).  This
     results in a noticeable speedup, but can be disabled by this
     option.

   It is often necessary to check the content of a 'configure.ac' file,
but parsing it yourself is extremely fragile and error-prone.  It is
suggested that you rely upon '--trace' to scan 'configure.ac'.

   The FORMAT of '--trace' can use the following special escapes:

'$$'
     The character '$'.

'$f'
     The filename from which MACRO is called.

'$l'
     The line number from which MACRO is called.

'$d'
     The depth of the MACRO call.  This is an M4 technical detail that
     you probably don't want to know about.

'$n'
     The name of the MACRO.

'$NUM'
     The NUMth argument of the call to MACRO.

'$@'
'$SEP@'
'${SEPARATOR}@'
     All the arguments passed to MACRO, separated by the character SEP
     or the string SEPARATOR (',' by default).  Each argument is quoted,
     i.e.  enclosed in a pair of square brackets.

'$*'
'$SEP*'
'${SEPARATOR}*'
     As above, but the arguments are not quoted.

'$%'
'$SEP%'
'${SEPARATOR}%'
     As above, but the arguments are not quoted, all new line characters
     in the arguments are smashed, and the default separator is ':'.

     The escape '$%' produces single-line trace outputs (unless you put
     newlines in the 'separator'), while '$@' and '$*' do not.

   For instance, to find the list of variables that are substituted,
use:

     $ autoconf -t AC_SUBST
     configure.ac:2:AC_SUBST:ECHO_C
     configure.ac:2:AC_SUBST:ECHO_N
     configure.ac:2:AC_SUBST:ECHO_T
     More traces deleted

The example below highlights the difference between '$@', '$*', and
*$%*.

     $ cat configure.ac
     AC_DEFINE(This, is, [an
     [example]])
     $ autoconf -t 'AC_DEFINE:@: $@
     *: $*
     $: $%'
     @: [This],[is],[an
     [example]]
     *: This,is,an
     [example]
     $: This:is:an [example]

The FORMAT gives you a lot of freedom:

     $ autoconf -t 'AC_SUBST:$$ac_subst{"$1"} = "$f:$l";'
     $ac_subst{"ECHO_C"} = "configure.ac:2";
     $ac_subst{"ECHO_N"} = "configure.ac:2";
     $ac_subst{"ECHO_T"} = "configure.ac:2";
     More traces deleted

A long SEPARATOR can be used to improve the readability of complex
structures, and to ease its parsing (for instance when no single
character is suitable as a separator)):

     $ autoconf -t 'AM_MISSING_PROG:${|:::::|}*'
     AUTOCONF|:::::|autoconf|:::::|$missing_dir
     More traces deleted


File: autoconf.info,  Node: autoreconf Invocation,  Prev: autoconf Invocation,  Up: Making configure Scripts

3.5 Using 'autoreconf' to Update 'configure' Scripts
====================================================

If you have a lot of Autoconf-generated 'configure' scripts, the
'autoreconf' program can save you some work.  It runs 'autoconf' (and
'autoheader', where appropriate) repeatedly to remake the Autoconf
'configure' scripts and configuration header templates in the directory
tree rooted at the current directory.  By default, it only remakes those
files that are older than their 'configure.ac' or (if present)
'aclocal.m4'.  Since 'autoheader' does not change the timestamp of its
output file if the file wouldn't be changing, this is not necessarily
the minimum amount of work.  If you install a new version of Autoconf,
you can make 'autoreconf' remake _all_ of the files by giving it the
'--force' option.

   If you give 'autoreconf' the '--autoconf-dir=DIR' or '--localdir=DIR'
options, it passes them down to 'autoconf' and 'autoheader' (with
relative paths adjusted properly).

   'autoreconf' does not support having, in the same directory tree,
both directories that are parts of a larger package (sharing
'aclocal.m4' and 'acconfig.h') and directories that are independent
packages (each with their own 'aclocal.m4' and 'acconfig.h').  It
assumes that they are all part of the same package if you use
'--localdir', or that each directory is a separate package if you don't
use it.  This restriction may be removed in the future.

   *Note Automatic Remaking::, for 'Makefile' rules to automatically
remake 'configure' scripts when their source files change.  That method
handles the timestamps of configuration header templates properly, but
does not pass '--autoconf-dir=DIR' or '--localdir=DIR'.

'autoreconf' accepts the following options:

'--help'
'-h'
     Print a summary of the command line options and exit.

'--version'
'-V'
     Print the version number of Autoconf and exit.

'--verbose'
     Print the name of each directory where 'autoreconf' runs 'autoconf'
     (and 'autoheader', if appropriate).

'--debug'
'-d'
     Don't remove the temporary files.

'--force'
'-f'
     Remake even 'configure' scripts and configuration headers that are
     newer than their input files ('configure.ac' and, if present,
     'aclocal.m4').

'--install'
'-i'
     Copy missing auxiliary files.  This option is similar to the option
     '--add-missing' in other tools.

'--symlink'
'-s'
     Instead of copying missing auxiliary files, install symbolic links.

'--localdir=DIR'
'-l DIR'
     Have 'autoconf' and 'autoheader' look for the package files
     'aclocal.m4' and ('autoheader' only) 'acconfig.h' (but not
     'FILE.top' and 'FILE.bot') in directory DIR instead of in the
     directory containing each 'configure.ac'.

'--autoconf-dir=DIR'
'-A DIR'
     Override the location where the installed Autoconf data files are
     looked for.  You can also set the 'AC_MACRODIR' environment
     variable to a directory; this option overrides the environment
     variable.

     This option is rarely needed and dangerous; it is only used when
     one plays with different versions of Autoconf simultaneously.

'--m4dir=DIR'
'-M DIR'
     Specify location of additional macro files ('m4' by default).


File: autoconf.info,  Node: Setup,  Next: Existing Tests,  Prev: Making configure Scripts,  Up: Top

4 Initialization and Output Files
*********************************

Autoconf-generated 'configure' scripts need some information about how
to initialize, such as how to find the package's source files; and about
the output files to produce.  The following sections describe
initialization and the creation of output files.

* Menu:

* Notices::                     Copyright, version numbers in 'configure'
* Input::                       Where Autoconf should find files
* Output::                      Outputting results from the configuration
* Configuration Actions::       Preparing the output based on results
* Configuration Files::         Creating output files
* Makefile Substitutions::      Using output variables in 'Makefile's
* Configuration Headers::       Creating a configuration header file
* Configuration Commands::      Running arbitrary instantiation commands
* Configuration Links::         Links depending from the configuration
* Subdirectories::              Configuring independent packages together
* Default Prefix::              Changing the default installation prefix


File: autoconf.info,  Node: Notices,  Next: Input,  Prev: Setup,  Up: Setup

4.1 Notices in 'configure'
==========================

The following macros manage version numbers for 'configure' scripts.
Using them is optional.

 -- Macro: AC_PREREQ (VERSION)
     Ensure that a recent enough version of Autoconf is being used.  If
     the version of Autoconf being used to create 'configure' is earlier
     than VERSION, print an error message to the standard error output
     and do not create 'configure'.  For example:

          AC_PREREQ(2.52.20240618)

     This macro is the only macro that may be used before 'AC_INIT', but
     for consistency, you are invited not to do so.

 -- Macro: AC_COPYRIGHT (COPYRIGHT-NOTICE)
     State that, in addition to the Free Software Foundation's copyright
     on the Autoconf macros, parts of your 'configure' are covered by
     the COPYRIGHT-NOTICE.

     The COPYRIGHT-NOTICE will show up in both the head of 'configure'
     and in 'configure --version'.

 -- Macro: AC_REVISION (REVISION-INFO)
     Copy revision stamp REVISION-INFO into the 'configure' script, with
     any dollar signs or double-quotes removed.  This macro lets you put
     a revision stamp from 'configure.ac' into 'configure' without RCS
     or 'cvs' changing it when you check in 'configure'.  That way, you
     can determine easily which revision of 'configure.ac' a particular
     'configure' corresponds to.

     For example, this line in 'configure.ac':

          AC_REVISION($Revision: 1.80 $)

     produces this in 'configure':

          #! /bin/sh
          # From configure.ac Revision: 1.30


File: autoconf.info,  Node: Input,  Next: Output,  Prev: Notices,  Up: Setup

4.2 Finding 'configure' Input
=============================

Every 'configure' script must call 'AC_INIT' before doing anything else.
The only other required macro is 'AC_OUTPUT' (*note Output::).

 -- Macro: AC_INIT (PACKAGE, VERSION, [BUG-REPORT-ADDRESS])
     Process any command-line arguments and perform various
     initializations and verifications.  Set the name of the PACKAGE and
     its VERSION.  The optional argument BUG-REPORT-ADDRESS should be
     the email to which users should send bug reports.

 -- Macro: AC_CONFIG_SRCDIR (UNIQUE-FILE-IN-SOURCE-DIR)
     UNIQUE-FILE-IN-SOURCE-DIR is some file that is in the package's
     source directory; 'configure' checks for this file's existence to
     make sure that the directory that it is told contains the source
     code in fact does.  Occasionally people accidentally specify the
     wrong directory with '--srcdir'; this is a safety check.  *Note
     configure Invocation::, for more information.

   Packages that do manual configuration or use the 'install' program
might need to tell 'configure' where to find some other shell scripts by
calling 'AC_CONFIG_AUX_DIR', though the default places it looks are
correct for most cases.

 -- Macro: AC_CONFIG_AUX_DIR (DIR)
     Use the auxiliary build tools (e.g., 'install-sh', 'config.sub',
     'config.guess', Cygnus 'configure', Automake and Libtool scripts
     etc.)  that are in directory DIR.  These are auxiliary files used
     in configuration.  DIR can be either absolute or relative to
     'SRCDIR'.  The default is 'SRCDIR' or 'SRCDIR/..' or
     'SRCDIR/../..', whichever is the first that contains 'install-sh'.
     The other files are not checked for, so that using
     'AC_PROG_INSTALL' does not automatically require distributing the
     other auxiliary files.  It checks for 'install.sh' also, but that
     name is obsolete because some 'make' have a rule that creates
     'install' from it if there is no 'Makefile'.


File: autoconf.info,  Node: Output,  Next: Configuration Actions,  Prev: Input,  Up: Setup

4.3 Outputting Files
====================

Every Autoconf-generated 'configure' script must finish by calling
'AC_OUTPUT'.  It is the macro that generates 'config.status', which will
create the 'Makefile's and any other files resulting from configuration.
The only other required macro is 'AC_INIT' (*note Input::).

 -- Macro: AC_OUTPUT
     Generate 'config.status' and launch it.  Call this macro once, at
     the end of 'configure.ac'.

     'config.status' will take all the configuration actions: all the
     output files (see *note Configuration Files::, macro
     'AC_CONFIG_FILES'), header files (see *note Configuration
     Headers::, macro 'AC_CONFIG_HEADERS'), commands (see *note
     Configuration Commands::, macro 'AC_CONFIG_COMMANDS'), links (see
     *note Configuration Links::, macro 'AC_CONFIG_LINKS'),
     subdirectories to configure (see *note Subdirectories::, macro
     'AC_CONFIG_SUBDIRS') are honored.

   Historically, the usage of 'AC_OUTPUT' was somewhat different.  *Note
Obsolete Macros::, for a description of the arguments that 'AC_OUTPUT'
used to support.

   If you run 'make' on subdirectories, you should run it using the
'make' variable 'MAKE'.  Most versions of 'make' set 'MAKE' to the name
of the 'make' program plus any options it was given.  (But many do not
include in it the values of any variables set on the command line, so
those are not passed on automatically.)  Some old versions of 'make' do
not set this variable.  The following macro allows you to use it even
with those versions.

 -- Macro: AC_PROG_MAKE_SET
     If 'make' predefines the variable 'MAKE', define output variable
     'SET_MAKE' to be empty.  Otherwise, define 'SET_MAKE' to contain
     'MAKE=make'.  Calls 'AC_SUBST' for 'SET_MAKE'.

   To use this macro, place a line like this in each 'Makefile.in' that
runs 'MAKE' on other directories:

     @SET_MAKE@


File: autoconf.info,  Node: Configuration Actions,  Next: Configuration Files,  Prev: Output,  Up: Setup

4.4 Taking Configuration Actions
================================

'configure' is designed so that it appears to do everything itself, but
there is actually a hidden slave: 'config.status'.  'configure' is in
charge of examining your system, but it is 'config.status' that actually
takes the proper actions based on the results of 'configure'.  The most
typical task of 'config.status' is to _instantiate_ files.

   This section describes the common behavior of the four standard
instantiating macros: 'AC_CONFIG_FILES', 'AC_CONFIG_HEADERS',
'AC_CONFIG_COMMANDS' and 'AC_CONFIG_LINKS'.  They all have this
prototype:

     AC_CONFIG_FOOS(TAG..., [COMMANDS], [INIT-CMDS])

where the arguments are:

TAG...
     A whitespace-separated list of tags, which are typically the names
     of the files to instantiate.

COMMANDS
     Shell commands output literally into 'config.status', and
     associated with a tag that the user can use to tell 'config.status'
     which the commands to run.  The commands are run each time a TAG
     request is given to 'config.status'; typically, each time the file
     'TAG' is created.

INIT-CMDS
     Shell commands output _unquoted_ near the beginning of
     'config.status', and executed each time 'config.status' runs
     (regardless of the tag).  Because they are unquoted, for example,
     '$var' will be output as the value of 'var'.  INIT-CMDS is
     typically used by 'configure' to give 'config.status' some
     variables it needs to run the COMMANDS.

   All these macros can be called multiple times, with different TAGs,
of course!

   You are encouraged to use literals as TAGS.  In particular, you
should avoid

     ... && my_foos="$my_foos fooo"
     ... && my_foos="$my_foos foooo"
     AC_CONFIG_FOOS($my_foos)

and use this instead:

     ... && AC_CONFIG_FOOS(fooo)
     ... && AC_CONFIG_FOOS(foooo)

   The macro 'AC_CONFIG_FILES' and 'AC_CONFIG_HEADERS' use specials
TAGs: they may have the form 'OUTPUT' or 'OUTPUT:INPUTS'.  The file
OUTPUT is instantiated from its templates, INPUTS if specified,
defaulting to 'OUTPUT.in'.

   For instance 'AC_CONFIG_FILES(Makefile:boiler/top.mk:boiler/bot.mk)'
asks for the creation of 'Makefile' that will be the expansion of the
output variables in the concatenation of 'boiler/top.mk' and
'boiler/bot.mk'.

   The special value '-' might be used to denote the standard output
when used in OUTPUT, or the standard input when used in the INPUTS.  You
most probably don't need to use this in 'configure.ac', but it is
convenient when using the command line interface of './config.status',
see *note config.status Invocation::, for more details.

   The INPUTS may be absolute or relative filenames.  In the latter case
they are first looked for in the build tree, and then in the source
tree.


File: autoconf.info,  Node: Configuration Files,  Next: Makefile Substitutions,  Prev: Configuration Actions,  Up: Setup

4.5 Creating Configuration Files
================================

Be sure to read the previous section, *note Configuration Actions::.

 -- Macro: AC_CONFIG_FILES (FILE..., [CMDS], [INIT-CMDS])
     Make 'AC_OUTPUT' create each 'FILE' by copying an input file (by
     default 'FILE.in'), substituting the output variable values.  This
     macro is one of the instantiating macros, see *note Configuration
     Actions::.  *Note Makefile Substitutions::, for more information on
     using output variables.  *Note Setting Output Variables::, for more
     information on creating them.  This macro creates the directory
     that the file is in if it doesn't exist.  Usually, 'Makefile's are
     created this way, but other files, such as '.gdbinit', can be
     specified as well.

     Typical calls to 'AC_CONFIG_FILES' look like this:

          AC_CONFIG_FILES(Makefile src/Makefile man/Makefile X/Imakefile)
          AC_CONFIG_FILES(autoconf, chmod +x autoconf)

     You can override an input file name by appending to FILE a
     colon-separated list of input files.  Examples:

          AC_CONFIG_FILES(Makefile:boiler/top.mk:boiler/bot.mk
                          lib/Makefile:boiler/lib.mk)

     Doing this allows you to keep your file names acceptable to MS-DOS,
     or to prepend and/or append boilerplate to the file.


File: autoconf.info,  Node: Makefile Substitutions,  Next: Configuration Headers,  Prev: Configuration Files,  Up: Setup

4.6 Substitutions in Makefiles
==============================

Each subdirectory in a distribution that contains something to be
compiled or installed should come with a file 'Makefile.in', from which
'configure' will create a 'Makefile' in that directory.  To create a
'Makefile', 'configure' performs a simple variable substitution,
replacing occurrences of '@VARIABLE@' in 'Makefile.in' with the value
that 'configure' has determined for that variable.  Variables that are
substituted into output files in this way are called "output variables".
They are ordinary shell variables that are set in 'configure'.  To make
'configure' substitute a particular variable into the output files, the
macro 'AC_SUBST' must be called with that variable name as an argument.
Any occurrences of '@VARIABLE@' for other variables are left unchanged.
*Note Setting Output Variables::, for more information on creating
output variables with 'AC_SUBST'.

   A software package that uses a 'configure' script should be
distributed with a file 'Makefile.in', but no 'Makefile'; that way, the
user has to properly configure the package for the local system before
compiling it.

   *Note Makefile Conventions: (standards)Makefile Conventions, for more
information on what to put in 'Makefile's.

* Menu:

* Preset Output Variables::     Output variables that are always set
* Installation Directory Variables::  Other preset output variables
* Build Directories::           Supporting multiple concurrent compiles
* Automatic Remaking::          Makefile rules for configuring


File: autoconf.info,  Node: Preset Output Variables,  Next: Installation Directory Variables,  Prev: Makefile Substitutions,  Up: Makefile Substitutions

4.6.1 Preset Output Variables
-----------------------------

Some output variables are preset by the Autoconf macros.  Some of the
Autoconf macros set additional output variables, which are mentioned in
the descriptions for those macros.  *Note Output Variable Index::, for a
complete list of output variables.  *Note Installation Directory
Variables::, for the list of the preset ones related to installation
directories.  Below are listed the other preset ones.  They all are
precious variables (*note Setting Output Variables::, 'AC_ARG_VAR').

 -- Variable: CFLAGS
     Debugging and optimization options for the C compiler.  If it is
     not set in the environment when 'configure' runs, the default value
     is set when you call 'AC_PROG_CC' (or empty if you don't).
     'configure' uses this variable when compiling programs to test for
     C features.

 -- Variable: configure_input
     A comment saying that the file was generated automatically by
     'configure' and giving the name of the input file.  'AC_OUTPUT'
     adds a comment line containing this variable to the top of every
     'Makefile' it creates.  For other files, you should reference this
     variable in a comment at the top of each input file.  For example,
     an input shell script should begin like this:

          #! /bin/sh
          # @configure_input@

     The presence of that line also reminds people editing the file that
     it needs to be processed by 'configure' in order to be used.

 -- Variable: CPPFLAGS
     Header file search directory ('-IDIR') and any other miscellaneous
     options for the C and C++ preprocessors and compilers.  If it is
     not set in the environment when 'configure' runs, the default value
     is empty.  'configure' uses this variable when compiling or
     preprocessing programs to test for C and C++ features.

 -- Variable: CXXFLAGS
     Debugging and optimization options for the C++ compiler.  If it is
     not set in the environment when 'configure' runs, the default value
     is set when you call 'AC_PROG_CXX' (or empty if you don't).
     'configure' uses this variable when compiling programs to test for
     C++ features.

 -- Variable: DEFS
     '-D' options to pass to the C compiler.  If 'AC_CONFIG_HEADERS' is
     called, 'configure' replaces '@DEFS@' with '-DHAVE_CONFIG_H'
     instead (*note Configuration Headers::).  This variable is not
     defined while 'configure' is performing its tests, only when
     creating the output files.  *Note Setting Output Variables::, for
     how to check the results of previous tests.

 -- Variable: ECHO_C
 -- Variable: ECHO_N
 -- Variable: ECHO_T
     How does one suppress the trailing newline from 'echo' for
     question-answer message pairs?  These variables provide a way:

          echo $ECHO_N "And the winner is... $ECHO_C"
          sleep 100000000000
          echo "${ECHO_T}dead."

     Some old and uncommon 'echo' implementations offer no means to
     achieve this, in which case 'ECHO_T' is set to tab.  You might not
     want to use it.

 -- Variable: FFLAGS
     Debugging and optimization options for the Fortran 77 compiler.  If
     it is not set in the environment when 'configure' runs, the default
     value is set when you call 'AC_PROG_F77' (or empty if you don't).
     'configure' uses this variable when compiling programs to test for
     Fortran 77 features.

 -- Variable: LDFLAGS
     Stripping ('-s'), path ('-L'), and any other miscellaneous options
     for the linker.  Don't use this variable to pass library names
     ('-l') to the linker, use 'LIBS' instead.  If it is not set in the
     environment when 'configure' runs, the default value is empty.
     'configure' uses this variable when linking programs to test for C,
     C++ and Fortran 77 features.

 -- Variable: LIBS
     '-l' options to pass to the linker.  The default value is empty,
     but some Autoconf macros may prepend extra libraries to this
     variable if those libraries are found and provide necessary
     functions, see *note Libraries::.  'configure' uses this variable
     when linking programs to test for C, C++ and Fortran 77 features.

 -- Variable: srcdir
     The directory that contains the source code for that 'Makefile'.

 -- Variable: top_srcdir
     The top-level source code directory for the package.  In the
     top-level directory, this is the same as 'srcdir'.


File: autoconf.info,  Node: Installation Directory Variables,  Next: Build Directories,  Prev: Preset Output Variables,  Up: Makefile Substitutions

4.6.2 Installation Directory Variables
--------------------------------------

The following variables specify the directories where the package will
be installed, see *note Variables for Installation Directories:
(standards)Directory Variables, for more information.  See the end of
this section for details on when and how to use these variables.

 -- Variable: bindir
     The directory for installing executables that users run.

 -- Variable: datadir
     The directory for installing read-only architecture-independent
     data.

 -- Variable: exec_prefix
     The installation prefix for architecture-dependent files.  By
     default it's the same as PREFIX.  You should avoid installing
     anything directly to EXEC_PREFIX.  However, the default value for
     directories containing architecture-dependent files should be
     relative to EXEC_PREFIX.

 -- Variable: includedir
     The directory for installing C header files.

 -- Variable: infodir
     The directory for installing documentation in Info format.

 -- Variable: libdir
     The directory for installing object code libraries.

 -- Variable: libexecdir
     The directory for installing executables that other programs run.

 -- Variable: localstatedir
     The directory for installing modifiable single-machine data.

 -- Variable: mandir
     The top-level directory for installing documentation in man format.

 -- Variable: oldincludedir
     The directory for installing C header files for non-gcc compilers.

 -- Variable: prefix
     The common installation prefix for all files.  If EXEC_PREFIX is
     defined to a different value, PREFIX is used only for
     architecture-independent files.

 -- Variable: sbindir
     The directory for installing executables that system administrators
     run.

 -- Variable: sharedstatedir
     The directory for installing modifiable architecture-independent
     data.

 -- Variable: sysconfdir
     The directory for installing read-only single-machine data.

   Most of these variables have values that rely on 'prefix' or
'exec_prefix'.  It is on purpose that the directory output variables
keep them unexpanded: typically '@datadir@' will be replaced by
'${prefix}/share', not '/usr/local/share'.

   This behavior is mandated by the GNU coding standards, so that when
the user runs:

'make'
     she can still specify a different prefix from the one specified to
     'configure', in which case, if needed, the package shall hard code
     dependencies to her late desires.

'make install'
     she can specify a different installation location, in which case
     the package _must_ still depend on the location which was compiled
     in (i.e., never recompile when 'make install' is run).  This is an
     extremely important feature, as many people may decide to install
     all the files of a package grouped together, and then install links
     from the final locations to there.

   In order to support these features, it is essential that 'datadir'
remains being defined as '${prefix}/share' to depend upon the current
value of 'prefix'.

   A corollary is that you should not use these variables but in
Makefiles.  For instance, instead of trying to evaluate 'datadir' in
'configure' and hardcoding it in Makefiles using e.g.
'AC_DEFINE_UNQUOTED(DATADIR, "$datadir")', you should add
'-DDATADIR="$(datadir)"' to your 'CPPFLAGS'.

   Similarly you should not rely on 'AC_OUTPUT_FILES' to replace
'datadir' and friends in your shell scripts and other files, rather let
'make' manage their replacement.  For instance Autoconf ships templates
of its shell scripts ending with '.sh', and uses this Makefile snippet:

     .sh:
             rm -f $@ $@.tmp
             sed 's,@datadir\@,$(pkgdatadir),g' $< >$@.tmp
             chmod +x $@.tmp
             mv $@.tmp $@

   Three things are noteworthy:

'@datadir\@'
     The backslash prevents 'configure' from replacing '@datadir@' in
     the sed expression itself.

'$(pkgdatadir)'
     Don't use '@pkgdatadir@'!  Use the matching makefile variable
     instead.

','
     Don't use '/' in the sed expression(s) since most probably the
     variables you use, such as '$(pkgdatadir)', will contain some.


File: autoconf.info,  Node: Build Directories,  Next: Automatic Remaking,  Prev: Installation Directory Variables,  Up: Makefile Substitutions

4.6.3 Build Directories
-----------------------

You can support compiling a software package for several architectures
simultaneously from the same copy of the source code.  The object files
for each architecture are kept in their own directory.

   To support doing this, 'make' uses the 'VPATH' variable to find the
files that are in the source directory.  GNU 'make' and most other
recent 'make' programs can do this.  Older 'make' programs do not
support 'VPATH'; when using them, the source code must be in the same
directory as the object files.

   To support 'VPATH', each 'Makefile.in' should contain two lines that
look like:

     srcdir = @srcdir@
     VPATH = @srcdir@

   Do not set 'VPATH' to the value of another variable, for example
'VPATH = $(srcdir)', because some versions of 'make' do not do variable
substitutions on the value of 'VPATH'.

   'configure' substitutes in the correct value for 'srcdir' when it
produces 'Makefile'.

   Do not use the 'make' variable '$<', which expands to the file name
of the file in the source directory (found with 'VPATH'), except in
implicit rules.  (An implicit rule is one such as '.c.o', which tells
how to create a '.o' file from a '.c' file.)  Some versions of 'make' do
not set '$<' in explicit rules; they expand it to an empty value.

   Instead, 'Makefile' command lines should always refer to source files
by prefixing them with '$(srcdir)/'.  For example:

     time.info: time.texinfo
             $(MAKEINFO) $(srcdir)/time.texinfo


File: autoconf.info,  Node: Automatic Remaking,  Prev: Build Directories,  Up: Makefile Substitutions

4.6.4 Automatic Remaking
------------------------

You can put rules like the following in the top-level 'Makefile.in' for
a package to automatically update the configuration information when you
change the configuration files.  This example includes all of the
optional files, such as 'aclocal.m4' and those related to configuration
header files.  Omit from the 'Makefile.in' rules for any of these files
that your package does not use.

   The '$(srcdir)/' prefix is included because of limitations in the
'VPATH' mechanism.

   The 'stamp-' files are necessary because the timestamps of
'config.h.in' and 'config.h' will not be changed if remaking them does
not change their contents.  This feature avoids unnecessary
recompilation.  You should include the file 'stamp-h.in' your package's
distribution, so 'make' will consider 'config.h.in' up to date.  Don't
use 'touch' (*note Limitations of Usual Tools::), rather use 'echo'
(using 'date' would cause needless differences, hence CVS conflicts
etc.).

     $(srcdir)/configure: configure.ac aclocal.m4
             cd $(srcdir) && autoconf

     # autoheader might not change config.h.in, so touch a stamp file.
     $(srcdir)/config.h.in: stamp-h.in
     $(srcdir)/stamp-h.in: configure.ac aclocal.m4
             cd $(srcdir) && autoheader
             echo timestamp > $(srcdir)/stamp-h.in

     config.h: stamp-h
     stamp-h: config.h.in config.status
             ./config.status

     Makefile: Makefile.in config.status
             ./config.status

     config.status: configure
             ./config.status --recheck

(Be careful if you copy these lines directly into your Makefile, as you
will need to convert the indented lines to start with the tab
character.)

   In addition, you should use 'AC_CONFIG_FILES(stamp-h, echo timestamp
> stamp-h)' so 'config.status' will ensure that 'config.h' is considered
up to date.  *Note Output::, for more information about 'AC_OUTPUT'.

   *Note config.status Invocation::, for more examples of handling
configuration-related dependencies.


File: autoconf.info,  Node: Configuration Headers,  Next: Configuration Commands,  Prev: Makefile Substitutions,  Up: Setup

4.7 Configuration Header Files
==============================

When a package tests more than a few C preprocessor symbols, the command
lines to pass '-D' options to the compiler can get quite long.  This
causes two problems.  One is that the 'make' output is hard to visually
scan for errors.  More seriously, the command lines can exceed the
length limits of some operating systems.  As an alternative to passing
'-D' options to the compiler, 'configure' scripts can create a C header
file containing '#define' directives.  The 'AC_CONFIG_HEADERS' macro
selects this kind of output.  It should be called right after 'AC_INIT'.

   The package should '#include' the configuration header file before
any other header files, to prevent inconsistencies in declarations (for
example, if it redefines 'const').  Use '#include <config.h>' instead of
'#include "config.h"', and pass the C compiler a '-I.' option (or
'-I..'; whichever directory contains 'config.h').  That way, even if the
source directory is configured itself (perhaps to make a distribution),
other build directories can also be configured without finding the
'config.h' from the source directory.

 -- Macro: AC_CONFIG_HEADERS (HEADER ..., [CMDS], [INIT-CMDS])
     This macro is one of the instantiating macros, see *note
     Configuration Actions::.  Make 'AC_OUTPUT' create the file(s) in
     the whitespace-separated list HEADER containing C preprocessor
     '#define' statements, and replace '@DEFS@' in generated files with
     '-DHAVE_CONFIG_H' instead of the value of 'DEFS'.  The usual name
     for HEADER is 'config.h'.

     If HEADER already exists and its contents are identical to what
     'AC_OUTPUT' would put in it, it is left alone.  Doing this allows
     some changes in configuration without needlessly causing object
     files that depend on the header file to be recompiled.

     Usually the input file is named 'HEADER.in'; however, you can
     override the input file name by appending to HEADER, a
     colon-separated list of input files.  Examples:

          AC_CONFIG_HEADERS(config.h:config.hin)
          AC_CONFIG_HEADERS(defines.h:defs.pre:defines.h.in:defs.post)

     Doing this allows you to keep your file names acceptable to MS-DOS,
     or to prepend and/or append boilerplate to the file.

   *Note Configuration Actions::, for more details on HEADER.

* Menu:

* Header Templates::            Input for the configuration headers
* autoheader Invocation::       How to create configuration templates
* Autoheader Macros::           How to specify CPP templates


File: autoconf.info,  Node: Header Templates,  Next: autoheader Invocation,  Prev: Configuration Headers,  Up: Configuration Headers

4.7.1 Configuration Header Templates
------------------------------------

Your distribution should contain a template file that looks as you want
the final header file to look, including comments, with '#undef'
statements which are used as hooks.  For example, suppose your
'configure.ac' makes these calls:

     AC_CONFIG_HEADERS(conf.h)
     AC_CHECK_HEADERS(unistd.h)

Then you could have code like the following in 'conf.h.in'.  On systems
that have 'unistd.h', 'configure' will '#define' 'HAVE_UNISTD_H' to 1.
On other systems, the whole line will be commented out (in case the
system predefines that symbol).

     /* Define as 1 if you have unistd.h.  */
     #undef HAVE_UNISTD_H

   You can then decode the configuration header using the preprocessor
directives:

     #include <conf.h>

     #if HAVE_UNISTD_H
     # include <unistd.h>
     #else
     /* We are in trouble. */
     #endif

   The use of old form templates, with '#define' instead of '#undef' is
strongly discouraged.

   Since it is a tedious task to keep a template header up to date, you
may use 'autoheader' to generate it, see *note autoheader Invocation::.


File: autoconf.info,  Node: autoheader Invocation,  Next: Autoheader Macros,  Prev: Header Templates,  Up: Configuration Headers

4.7.2 Using 'autoheader' to Create 'config.h.in'
------------------------------------------------

The 'autoheader' program can create a template file of C '#define'
statements for 'configure' to use.  If 'configure.ac' invokes
'AC_CONFIG_HEADERS(FILE)', 'autoheader' creates 'FILE.in'; if multiple
file arguments are given, the first one is used.  Otherwise,
'autoheader' creates 'config.h.in'.

   In order to do its job, 'autoheader' needs you to document all of the
symbols that you might use; i.e., there must be at least one 'AC_DEFINE'
or one 'AC_DEFINE_UNQUOTED' using its third argument for each symbol
(*note Defining Symbols::).  An additional constraint is that the first
argument of 'AC_DEFINE' must be a literal.  Note that all symbols
defined by Autoconf's built-in tests are already documented properly;
you only need to document those that you define yourself.

   You might wonder why 'autoheader' is needed: after all, why would
'configure' need to "patch" a 'config.h.in' to produce a 'config.h'
instead of just creating 'config.h' from scratch?  Well, when everything
rocks, the answer is just that we are wasting our time maintaining
'autoheader': generating 'config.h' directly is all that is needed.
When things go wrong, however, you'll be thankful for the existence of
'autoheader'.

   The fact that the symbols are documented is important in order to
_check_ that 'config.h' makes sense.  The fact that there is a well
defined list of symbols that should be '#define''d (or not) is also
important for people who are porting packages to environments where
'configure' cannot be run: they just have to _fill in the blanks_.

   But let's come back to the point: 'autoheader''s invocation...

   If you give 'autoheader' an argument, it uses that file instead of
'configure.ac' and writes the header file to the standard output instead
of to 'config.h.in'.  If you give 'autoheader' an argument of '-', it
reads the standard input instead of 'configure.ac' and writes the header
file to the standard output.

   'autoheader' accepts the following options:

'--help'
'-h'
     Print a summary of the command line options and exit.

'--version'
'-V'
     Print the version number of Autoconf and exit.

'--debug'
'-d'
     Don't remove the temporary files.

'--verbose'
'-v'
     Report processing steps.

'--autoconf-dir=DIR'
'-A DIR'
     Override the location where the installed Autoconf data files are
     looked for.  You can also set the 'AC_MACRODIR' environment
     variable to a directory; this option overrides the environment
     variable.

     This option is rarely needed and dangerous; it is only used when
     one plays with different versions of Autoconf simultaneously.

'--localdir=DIR'
'-l DIR'
     Look for the package files 'aclocal.m4' and 'acconfig.h' (but not
     'FILE.top' and 'FILE.bot') in directory DIR instead of in the
     current directory.

'--warnings=CATEGORY'
'-W CATEGORY'
     Report the warnings related to CATEGORY (which can actually be a
     comma separated list).  Current categories include:

     'obsolete'
          report the uses of obsolete constructs

     'all'
          report all the warnings

     'none'
          report none

     'error'
          treats warnings as errors

     'no-CATEGORY'
          disable warnings falling into CATEGORY


File: autoconf.info,  Node: Autoheader Macros,  Prev: autoheader Invocation,  Up: Configuration Headers

4.7.3 Autoheader Macros
-----------------------

'autoheader' scans 'configure.ac' and figures out which C preprocessor
symbols it might define.  It knows how to generate templates for symbols
defined by 'AC_CHECK_HEADERS', 'AC_CHECK_FUNCS' etc., but if you
'AC_DEFINE' any additional symbol, you must define a template for it.
If there are missing templates, 'autoheader' fails with an error
message.

   The simplest way to create a template for a SYMBOL is to supply the
DESCRIPTION argument to an 'AC_DEFINE(SYMBOL)'; see *note Defining
Symbols::.  You may also use one of the following macros.

 -- Macro: AH_VERBATIM (KEY, TEMPLATE)
     Tell 'autoheader' to include the TEMPLATE as-is in the header
     template file.  This TEMPLATE is associated with the KEY, which is
     used to sort all the different templates and guarantee their
     uniqueness.  It should be the symbol that can be 'AC_DEFINE''d.

     For example:

          AH_VERBATIM([_GNU_SOURCE],
          [/* Enable GNU extensions on systems that have them.  */
          #ifndef _GNU_SOURCE
          # define _GNU_SOURCE
          #endif])

 -- Macro: AH_TEMPLATE (KEY, DESCRIPTION)
     Tell 'autoheader' to generate a template for KEY.  This macro
     generates standard templates just like 'AC_DEFINE' when a
     DESCRIPTION is given.

     For example:

          AH_TEMPLATE([CRAY_STACKSEG_END],
                      [Define to one of _getb67, GETB67, getb67
                       for Cray-2 and Cray-YMP systems.  This
                       function is required for alloca.c support
                       on those systems.])

     will generate the following template, with the description properly
     justified.

          /* Define to one of _getb67, GETB67, getb67 for Cray-2 and
             Cray-YMP systems. This function is required for alloca.c
             support on those systems. */
          #undef CRAY_STACKSEG_END

 -- Macro: AH_TOP (TEXT)
     Include TEXT at the top of the header template file.

 -- Macro: AH_BOTTOM (TEXT)
     Include TEXT at the bottom of the header template file.


File: autoconf.info,  Node: Configuration Commands,  Next: Configuration Links,  Prev: Configuration Headers,  Up: Setup

4.8 Running Arbitrary Configuration Commands
============================================

You execute arbitrary commands either before, during and after
'config.status' is run.  The three following macros accumulate the
commands to run when they are called multiple times.
'AC_CONFIG_COMMANDS' replaces the obsolete macro 'AC_OUTPUT_COMMANDS',
see *note Obsolete Macros::, for details.

 -- Macro: AC_CONFIG_COMMANDS (TAG..., [CMDS], [INIT-CMDS])
     Specify additional shell commands to run at the end of
     'config.status', and shell commands to initialize any variables
     from 'configure'.  Associate the commands to the TAG.  Since
     typically the CMDS create a file, TAG should naturally be the name
     of that file.  This macro is one of the instantiating macros, see
     *note Configuration Actions::.

     Here is an unrealistic example:
          fubar=42
          AC_CONFIG_COMMANDS(fubar,
                             [echo this is extra $fubar, and so on.],
                             [fubar=$fubar])

     Here is a better one:
          AC_CONFIG_COMMANDS(time-stamp, [date >time-stamp])

 -- Macro: AC_CONFIG_COMMANDS_PRE (CMDS)
     Execute the CMDS right before creating 'config.status'.  A typical
     use is computing values derived from variables built during the
     execution of 'configure':

          AC_CONFIG_COMMANDS_PRE(
          [LTLIBOBJS=`echo $LIBOBJS | sed 's/\.o/\.lo/g'`
          AC_SUBST(LTLIBOBJS)])

 -- Macro: AC_CONFIG_COMMANDS_POST (CMDS)
     Execute the CMDS right after creating 'config.status'.


File: autoconf.info,  Node: Configuration Links,  Next: Subdirectories,  Prev: Configuration Commands,  Up: Setup

4.9 Creating Configuration Links
================================

You may find it convenient to create links whose destinations depend
upon results of tests.  One can use 'AC_CONFIG_COMMANDS' but the
creation of relative symbolic links can be delicate when the package is
built in another directory than its sources.

 -- Macro: AC_CONFIG_LINKS (DEST:SOURCE..., [CMDS], [INIT-CMDS])
     Make 'AC_OUTPUT' link each of the existing files SOURCE to the
     corresponding link name DEST.  Makes a symbolic link if possible,
     otherwise a hard link.  The DEST and SOURCE names should be
     relative to the top level source or build directory.  This macro is
     one of the instantiating macros, see *note Configuration Actions::.

     For example, this call:

          AC_CONFIG_LINKS(host.h:config/$machine.h
                          object.h:config/$obj_format.h)

     creates in the current directory 'host.h' as a link to
     'SRCDIR/config/$machine.h', and 'object.h' as a link to
     'SRCDIR/config/$obj_format.h'.

     The tempting value '.' for DEST is invalid: it makes it impossible
     for 'config.status' to guess the links to establish.

     One can then run:
          ./config.status host.h object.h
     to create the links.


File: autoconf.info,  Node: Subdirectories,  Next: Default Prefix,  Prev: Configuration Links,  Up: Setup

4.10 Configuring Other Packages in Subdirectories
=================================================

In most situations, calling 'AC_OUTPUT' is sufficient to produce
'Makefile's in subdirectories.  However, 'configure' scripts that
control more than one independent package can use 'AC_CONFIG_SUBDIRS' to
run 'configure' scripts for other packages in subdirectories.

 -- Macro: AC_CONFIG_SUBDIRS (DIR ...)
     Make 'AC_OUTPUT' run 'configure' in each subdirectory DIR in the
     given whitespace-separated list.  Each DIR should be a literal,
     i.e., please do not use:

          if test "$package_foo_enabled" = yes; then
            $my_subdirs="$my_subdirs foo"
          fi
          AC_CONFIG_SUBDIRS($my_subdirs)

     because this prevents './configure --help=recursive' from
     displaying the options of the package 'foo'.  Rather, you should
     write:

          if test "$package_foo_enabled" = yes then;
            AC_CONFIG_SUBDIRS(foo)
          fi

     If a given DIR is not found, no error is reported, so a 'configure'
     script can configure whichever parts of a large source tree are
     present.  If a given DIR contains 'configure.gnu', it is run
     instead of 'configure'.  This is for packages that might use a
     non-autoconf script 'Configure', which can't be called through a
     wrapper 'configure' since it would be the same file on
     case-insensitive filesystems.  Likewise, if a DIR contains
     'configure.ac' but no 'configure', the Cygnus 'configure' script
     found by 'AC_CONFIG_AUX_DIR' is used.

     The subdirectory 'configure' scripts are given the same command
     line options that were given to this 'configure' script, with minor
     changes if needed (e.g., to adjust a relative path for the cache
     file or source directory).  This macro also sets the output
     variable 'subdirs' to the list of directories 'DIR ...'.
     'Makefile' rules can use this variable to determine which
     subdirectories to recurse into.  This macro may be called multiple
     times.


File: autoconf.info,  Node: Default Prefix,  Prev: Subdirectories,  Up: Setup

4.11 Default Prefix
===================

By default, 'configure' sets the prefix for files it installs to
'/usr/local'.  The user of 'configure' can select a different prefix
using the '--prefix' and '--exec-prefix' options.  There are two ways to
change the default: when creating 'configure', and when running it.

   Some software packages might want to install in a directory besides
'/usr/local' by default.  To accomplish that, use the
'AC_PREFIX_DEFAULT' macro.

 -- Macro: AC_PREFIX_DEFAULT (PREFIX)
     Set the default installation prefix to PREFIX instead of
     '/usr/local'.

   It may be convenient for users to have 'configure' guess the
installation prefix from the location of a related program that they
have already installed.  If you wish to do that, you can call
'AC_PREFIX_PROGRAM'.

 -- Macro: AC_PREFIX_PROGRAM (PROGRAM)
     If the user did not specify an installation prefix (using the
     '--prefix' option), guess a value for it by looking for PROGRAM in
     'PATH', the way the shell does.  If PROGRAM is found, set the
     prefix to the parent of the directory containing PROGRAM; otherwise
     leave the prefix specified in 'Makefile.in' unchanged.  For
     example, if PROGRAM is 'gcc' and the 'PATH' contains
     '/usr/local/gnu/bin/gcc', set the prefix to '/usr/local/gnu'.


File: autoconf.info,  Node: Existing Tests,  Next: Writing Tests,  Prev: Setup,  Up: Top

5 Existing Tests
****************

These macros test for particular system features that packages might
need or want to use.  If you need to test for a kind of feature that
none of these macros check for, you can probably do it by calling
primitive test macros with appropriate arguments (*note Writing
Tests::).

   These tests print messages telling the user which feature they're
checking for, and what they find.  They cache their results for future
'configure' runs (*note Caching Results::).

   Some of these macros set output variables.  *Note Makefile
Substitutions::, for how to get their values.  The phrase "define NAME"
is used below as a shorthand to mean "define C preprocessor symbol NAME
to the value 1".  *Note Defining Symbols::, for how to get those symbol
definitions into your program.

* Menu:

* Common Behavior::             Macros' standard schemes
* Alternative Programs::        Selecting between alternative programs
* Files::                       Checking for the existence of files
* Libraries::                   Library archives that might be missing
* Library Functions::           C library functions that might be missing
* Header Files::                Header files that might be missing
* Declarations::                Declarations that may be missing
* Structures::                  Structures or members that might be missing
* Types::                       Types that might be missing
* Compilers and Preprocessors::  Checking for compiling programs
* System Services::             Operating system services
* UNIX Variants::               Special kludges for specific UNIX variants


File: autoconf.info,  Node: Common Behavior,  Next: Alternative Programs,  Prev: Existing Tests,  Up: Existing Tests

5.1 Common Behavior
===================

Much effort has been expended to make Autoconf easy to learn.  The most
obvious way to reach this goal is simply to enforce standard interfaces
and behaviors, avoiding exceptions as much as possible.  Because of
history and inertia, unfortunately, there are still too many exceptions
in Autoconf; nevertheless, this section describes some of the common
rules.

* Menu:

* Standard Symbols::            Symbols defined by the macros
* Default Includes::            Includes used by the generic macros


File: autoconf.info,  Node: Standard Symbols,  Next: Default Includes,  Prev: Common Behavior,  Up: Common Behavior

5.1.1 Standard Symbols
----------------------

All the generic macros that 'AC_DEFINE' a symbol as a result of their
test transform their ARGUMENTs to a standard alphabet.  First, ARGUMENT
is converted to upper case and any asterisks ('*') are each converted to
'P'.  Any remaining characters that are not alphanumeric are converted
to underscores.

   For instance,

     AC_CHECK_TYPES(struct $Expensive*)

will define the symbol 'HAVE_STRUCT__EXPENSIVEP' if the check succeeds.


File: autoconf.info,  Node: Default Includes,  Prev: Standard Symbols,  Up: Common Behavior

5.1.2 Default Includes
----------------------

Several tests depend upon a set of header files.  Since these headers
are not universally available, tests actually have to provide a set of
protected includes, such as:

     #if TIME_WITH_SYS_TIME
     # include <sys/time.h>
     # include <time.h>
     #else
     # if HAVE_SYS_TIME_H
     #  include <sys/time.h>
     # else
     #  include <time.h>
     # endif
     #endif

Unless you know exactly what you are doing, you should avoid using
unconditional includes, and check the existence of the headers you
include beforehand (*note Header Files::).

   Most generic macros provide the following default set of includes:

     #include <stdio.h>
     #if HAVE_SYS_TYPES_H
     # include <sys/types.h>
     #endif
     #if HAVE_SYS_STAT_H
     # include <sys/stat.h>
     #endif
     #if STDC_HEADERS
     # include <stdlib.h>
     # include <stddef.h>
     #else
     # if HAVE_STDLIB_H
     #  include <stdlib.h>
     # endif
     #endif
     #if HAVE_STRING_H
     # if !STDC_HEADERS && HAVE_MEMORY_H
     #  include <memory.h>
     # endif
     # include <string.h>
     #endif
     #if HAVE_STRINGS_H
     # include <strings.h>
     #endif
     #if HAVE_INTTYPES_H
     # include <inttypes.h>
     #else
     # if HAVE_STDINT_H
     #  include <stdint.h>
     # endif
     #endif
     #if HAVE_UNISTD_H
     # include <unistd.h>
     #endif

   If the default includes are used, then Autoconf will automatically
check for the presence of these headers and their compatibility, i.e.,
you don't need to run 'AC_HEADERS_STDC', nor check for 'stdlib.h' etc.

   These headers are checked for in the same order as they are included.
For instance, on some systems 'string.h' and 'strings.h' both exist, but
conflict.  Then 'HAVE_STRING_H' will be defined, but 'HAVE_STRINGS_H'
won't.


File: autoconf.info,  Node: Alternative Programs,  Next: Files,  Prev: Common Behavior,  Up: Existing Tests

5.2 Alternative Programs
========================

These macros check for the presence or behavior of particular programs.
They are used to choose between several alternative programs and to
decide what to do once one has been chosen.  If there is no macro
specifically defined to check for a program you need, and you don't need
to check for any special properties of it, then you can use one of the
general program-check macros.

* Menu:

* Particular Programs::         Special handling to find certain programs
* Generic Programs::            How to find other programs


File: autoconf.info,  Node: Particular Programs,  Next: Generic Programs,  Prev: Alternative Programs,  Up: Alternative Programs

5.2.1 Particular Program Checks
-------------------------------

These macros check for particular programs--whether they exist, and in
some cases whether they support certain features.

 -- Macro: AC_PROG_AWK
     Check for 'mawk', 'gawk', 'nawk', and 'awk', in that order, and set
     output variable 'AWK' to the first one that is found.  It tries
     'mawk' first because that is reported to be the fastest
     implementation.

 -- Macro: AC_PROG_EGREP
     Check for 'grep -E', 'egrep' in that order, and set output variable
     'EGREP' to the first one that is found.

 -- Macro: AC_PROG_FGREP
     Check for 'grep -F', 'fgrep' in that order, and set output variable
     'FGREP' to the first one that is found.

 -- Macro: AC_PROG_GREP
     Check for 'grep', 'ggrep' in that order, and set output variable
     'GREP' to the first one that is found.

 -- Macro: AC_PROG_INSTALL
     Set output variable 'INSTALL' to the path of a BSD compatible
     'install' program, if one is found in the current 'PATH'.
     Otherwise, set 'INSTALL' to 'DIR/install-sh -c', checking the
     directories specified to 'AC_CONFIG_AUX_DIR' (or its default
     directories) to determine DIR (*note Output::).  Also set the
     variables 'INSTALL_PROGRAM' and 'INSTALL_SCRIPT' to '${INSTALL}'
     and 'INSTALL_DATA' to '${INSTALL} -m 644'.

     This macro screens out various instances of 'install' known not to
     work.  It prefers to find a C program rather than a shell script,
     for speed.  Instead of 'install-sh', it can also use 'install.sh',
     but that name is obsolete because some 'make' programs have a rule
     that creates 'install' from it if there is no 'Makefile'.

     Autoconf comes with a copy of 'install-sh' that you can use.  If
     you use 'AC_PROG_INSTALL', you must include either 'install-sh' or
     'install.sh' in your distribution, or 'configure' will produce an
     error message saying it can't find them--even if the system you're
     on has a good 'install' program.  This check is a safety measure to
     prevent you from accidentally leaving that file out, which would
     prevent your package from installing on systems that don't have a
     BSD-compatible 'install' program.

     If you need to use your own installation program because it has
     features not found in standard 'install' programs, there is no
     reason to use 'AC_PROG_INSTALL'; just put the file name of your
     program into your 'Makefile.in' files.

 -- Macro: AC_PROG_LEX
     If 'flex' is found, set output variable 'LEX' to 'flex' and
     'LEXLIB' to '-lfl', if that library is in a standard place.
     Otherwise set 'LEX' to 'lex' and 'LEXLIB' to '-ll'.

     Define 'YYTEXT_POINTER' if 'yytext' is a 'char *' instead of a
     'char []'.  Also set output variable 'LEX_OUTPUT_ROOT' to the base
     of the file name that the lexer generates; usually 'lex.yy', but
     sometimes something else.  These results vary according to whether
     'lex' or 'flex' is being used.

     You are encouraged to use Flex in your sources, since it is both
     more pleasant to use than plain Lex and the C source it produces is
     portable.  In order to ensure portability, however, you must either
     provide a function 'yywrap' or, if you don't use it (e.g., your
     scanner has no '#include'-like feature), simply include a
     '%noyywrap' statement in the scanner's source.  Once this done, the
     scanner is portable (unless _you_ felt free to use nonportable
     constructs) and does not depend on any library.  In this case, and
     in this case only, it is suggested that you use this Autoconf
     snippet:

          AC_PROG_LEX
          if test "$LEX" != flex; then
            LEX="$SHELL $missing_dir/missing flex"
            AC_SUBST(LEX_OUTPUT_ROOT, lex.yy)
            AC_SUBST(LEXLIB, '')
          fi

     The shell script 'missing' can be found in the Automake
     distribution.

     To ensure backward compatibility, Automake's 'AM_PROG_LEX' invokes
     (indirectly) this macro twice, which will cause an annoying but
     benign "'AC_PROG_LEX' invoked multiple times" warning.  Future
     versions of Automake will fix this issue, meanwhile, just ignore
     this message.

 -- Macro: AC_PROG_LN_S
     If 'ln -s' works on the current file system (the operating system
     and file system support symbolic links), set the output variable
     'LN_S' to 'ln -s'; otherwise, if 'ln' works, set 'LN_S' to 'ln' and
     otherwise set it to 'cp -p'.

     If you make a link a directory other than the current directory,
     its meaning depends on whether 'ln' or 'ln -s' is used.  To safely
     create links using '$(LN_S)', either find out which form is used
     and adjust the arguments, or always invoke 'ln' in the directory
     where the link is to be created.

     In other words, it does not work to do:
          $(LN_S) foo /x/bar

     Instead, do:

          (cd /x && $(LN_S) foo bar)

 -- Macro: AC_PROG_RANLIB
     Set output variable 'RANLIB' to 'ranlib' if 'ranlib' is found, and
     otherwise to ':' (do nothing).

 -- Macro: AC_PROG_YACC
     If 'byacc' is found, set 'YACC' to 'byacc'.  Otherwise, if 'bison'
     is found, set output variable 'YACC' to 'bison -y'.  Finally, if
     neither 'byacc' or 'bison' is found, set 'YACC' to 'yacc'.


File: autoconf.info,  Node: Generic Programs,  Prev: Particular Programs,  Up: Alternative Programs

5.2.2 Generic Program and File Checks
-------------------------------------

These macros are used to find programs not covered by the "particular"
test macros.  If you need to check the behavior of a program as well as
find out whether it is present, you have to write your own test for it
(*note Writing Tests::).  By default, these macros use the environment
variable 'PATH'.  If you need to check for a program that might not be
in the user's 'PATH', you can pass a modified path to use instead, like
this:

     AC_PATH_PROG(INETD, inetd, /usr/libexec/inetd,
       $PATH:/usr/libexec:/usr/sbin:/usr/etc:etc)

   You are strongly encouraged to declare the VARIABLE passed to
'AC_CHECK_PROG' etc.  as precious, *Note Setting Output Variables::,
'AC_ARG_VAR', for more details.

 -- Macro: AC_CHECK_PROG (VARIABLE, PROG-TO-CHECK-FOR, VALUE-IF-FOUND,
          [VALUE-IF-NOT-FOUND], [PATH], [REJECT])
     Check whether program PROG-TO-CHECK-FOR exists in 'PATH'.  If it is
     found, set VARIABLE to VALUE-IF-FOUND, otherwise to
     VALUE-IF-NOT-FOUND, if given.  Always pass over REJECT (an absolute
     file name) even if it is the first found in the search path; in
     that case, set VARIABLE using the absolute file name of the
     PROG-TO-CHECK-FOR found that is not REJECT.  If VARIABLE was
     already set, do nothing.  Calls 'AC_SUBST' for VARIABLE.

 -- Macro: AC_CHECK_PROGS (VARIABLE, PROGS-TO-CHECK-FOR,
          [VALUE-IF-NOT-FOUND], [PATH])
     Check for each program in the whitespace-separated list
     PROGS-TO-CHECK-FOR exists on the 'PATH'.  If it is found, set
     VARIABLE to the name of that program.  Otherwise, continue checking
     the next program in the list.  If none of the programs in the list
     are found, set VARIABLE to VALUE-IF-NOT-FOUND; if
     VALUE-IF-NOT-FOUND is not specified, the value of VARIABLE is not
     changed.  Calls 'AC_SUBST' for VARIABLE.

 -- Macro: AC_CHECK_TOOL (VARIABLE, PROG-TO-CHECK-FOR,
          [VALUE-IF-NOT-FOUND], [PATH])
     Like 'AC_CHECK_PROG', but first looks for PROG-TO-CHECK-FOR with a
     prefix of the host type as determined by 'AC_CANONICAL_HOST',
     followed by a dash (*note Canonicalizing::).  For example, if the
     user runs 'configure --host=i386-gnu', then this call:
          AC_CHECK_TOOL(RANLIB, ranlib, :)
     sets 'RANLIB' to 'i386-gnu-ranlib' if that program exists in
     'PATH', or otherwise to 'ranlib' if that program exists in 'PATH',
     or to ':' if neither program exists.

 -- Macro: AC_CHECK_TOOLS (VARIABLE, PROGS-TO-CHECK-FOR,
          [VALUE-IF-NOT-FOUND], [PATH])
     Like 'AC_CHECK_TOOL', each of the tools in the list
     PROGS-TO-CHECK-FOR are checked with a prefix of the host type as
     determined by 'AC_CANONICAL_HOST', followed by a dash (*note
     Canonicalizing::).  If none of the tools can be found with a
     prefix, then the first one without a prefix is used.  If a tool is
     found, set VARIABLE to the name of that program.  If none of the
     tools in the list are found, set VARIABLE to VALUE-IF-NOT-FOUND; if
     VALUE-IF-NOT-FOUND is not specified, the value of VARIABLE is not
     changed.  Calls 'AC_SUBST' for VARIABLE.

 -- Macro: AC_PATH_PROG (VARIABLE, PROG-TO-CHECK-FOR,
          [VALUE-IF-NOT-FOUND], [PATH])
     Like 'AC_CHECK_PROG', but set VARIABLE to the entire path of
     PROG-TO-CHECK-FOR if found.

 -- Macro: AC_PATH_PROGS (VARIABLE, PROGS-TO-CHECK-FOR,
          [VALUE-IF-NOT-FOUND], [PATH])
     Like 'AC_CHECK_PROGS', but if any of PROGS-TO-CHECK-FOR are found,
     set VARIABLE to the entire path of the program found.

 -- Macro: AC_PATH_TOOL (VARIABLE, PROG-TO-CHECK-FOR,
          [VALUE-IF-NOT-FOUND], [PATH])
     Like 'AC_CHECK_TOOL', but set VARIABLE to the entire path of the
     program if it is found.


File: autoconf.info,  Node: Files,  Next: Libraries,  Prev: Alternative Programs,  Up: Existing Tests

5.3 Files
=========

You might also need to check for the existence of files.  Before using
these macros, ask yourself whether a run time test might not be a better
solution.  Be aware that, like most Autoconf macros, they test a feature
of the host machine, and therefore, they die when cross-compiling.

 -- Macro: AC_CHECK_FILE (FILE, [ACTION-IF-FOUND],
          [ACTION-IF-NOT-FOUND])
     Check whether file FILE exists on the native system.  If it is
     found, execute ACTION-IF-FOUND, otherwise do ACTION-IF-NOT-FOUND,
     if given.

 -- Macro: AC_CHECK_FILES (FILES, [ACTION-IF-FOUND],
          [ACTION-IF-NOT-FOUND])
     Executes 'AC_CHECK_FILE' once for each file listed in FILES.
     Additionally, defines 'HAVE_FILE' (*note Standard Symbols::) for
     each file found.


File: autoconf.info,  Node: Libraries,  Next: Library Functions,  Prev: Files,  Up: Existing Tests

5.4 Library Files
=================

The following macros check for the presence of certain C, C++ or Fortran
77 library archive files.

 -- Macro: AC_CHECK_LIB (LIBRARY, FUNCTION, [ACTION-IF-FOUND],
          [ACTION-IF-NOT-FOUND], [OTHER-LIBRARIES])
     Depending on the current language(*note Language Choice::), try to
     ensure that the C, C++, or Fortran 77 function FUNCTION is
     available by checking whether a test program can be linked with the
     library LIBRARY to get the function.  LIBRARY is the base name of
     the library; e.g., to check for '-lmp', use 'mp' as the LIBRARY
     argument.

     ACTION-IF-FOUND is a list of shell commands to run if the link with
     the library succeeds; ACTION-IF-NOT-FOUND is a list of shell
     commands to run if the link fails.  If ACTION-IF-FOUND is not
     specified, the default action will prepend '-lLIBRARY' to 'LIBS'
     and define 'HAVE_LIBLIBRARY' (in all capitals).  This macro is
     intended to support building of 'LIBS' in a right-to-left
     (least-dependent to most-dependent) fashion such that library
     dependencies are satisfied as a natural side-effect of consecutive
     tests.  Some linkers are very sensitive to library ordering so the
     order in which 'LIBS' is generated is important to reliable
     detection of libraries.

     If linking with LIBRARY results in unresolved symbols that would be
     resolved by linking with additional libraries, give those libraries
     as the OTHER-LIBRARIES argument, separated by spaces: e.g.  '-lXt
     -lX11'.  Otherwise, this macro will fail to detect that LIBRARY is
     present, because linking the test program will always fail with
     unresolved symbols.  The OTHER-LIBRARIES argument should be limited
     to cases where it is desirable to test for one library in the
     presence of another that is not already in 'LIBS'.

 -- Macro: AC_SEARCH_LIBS (FUNCTION, SEARCH-LIBS, [ACTION-IF-FOUND],
          [ACTION-IF-NOT-FOUND], [OTHER-LIBRARIES])
     Search for a library defining FUNCTION if it's not already
     available.  This equates to calling 'AC_TRY_LINK_FUNC' first with
     no libraries, then for each library listed in SEARCH-LIBS.

     Add '-lLIBRARY' to 'LIBS' for the first library found to contain
     FUNCTION, and run ACTION-IF-FOUND.  If the function is not found,
     run ACTION-IF-NOT-FOUND.

     If linking with LIBRARY results in unresolved symbols that would be
     resolved by linking with additional libraries, give those libraries
     as the OTHER-LIBRARIES argument, separated by spaces: e.g.  '-lXt
     -lX11'.  Otherwise, this macro will fail to detect that FUNCTION is
     present, because linking the test program will always fail with
     unresolved symbols.


File: autoconf.info,  Node: Library Functions,  Next: Header Files,  Prev: Libraries,  Up: Existing Tests

5.5 Library Functions
=====================

The following macros check for particular C library functions.  If there
is no macro specifically defined to check for a function you need, and
you don't need to check for any special properties of it, then you can
use one of the general function-check macros.

* Menu:

* Function Portability::        Pitfalls with usual functions
* Particular Functions::        Special handling to find certain functions
* Generic Functions::           How to find other functions


File: autoconf.info,  Node: Function Portability,  Next: Particular Functions,  Prev: Library Functions,  Up: Library Functions

5.5.1 Portability of Classical Functions
----------------------------------------

Most usual functions can either be missing, or be buggy, or be limited
on some architectures.  This section tries to make an inventory of these
portability issues.  By definition, this list will always require
additions, please help us keeping it as complete as possible

'unlink'
     The POSIX spec says that 'unlink' causes the given files to be
     removed only after there are no more open file handles for it.  Not
     all OS's support this behaviour though.  So even on systems that
     provide 'unlink', you cannot portably assume it is OK to call it on
     files that are open.  For example, on Windows 9x and ME, such a
     call would fail; on DOS it could even lead to file system
     corruption, as the file might end up being written to after the OS
     has removed it.


File: autoconf.info,  Node: Particular Functions,  Next: Generic Functions,  Prev: Function Portability,  Up: Library Functions

5.5.2 Particular Function Checks
--------------------------------

These macros check for particular C functions--whether they exist, and
in some cases how they respond when given certain arguments.

 -- Macro: AC_FUNC_ALLOCA
     Check how to get 'alloca'.  Tries to get a builtin version by
     checking for 'alloca.h' or the predefined C preprocessor macros
     '__GNUC__' and '_AIX'.  If this macro finds 'alloca.h', it defines
     'HAVE_ALLOCA_H'.

     If those attempts fail, it looks for the function in the standard C
     library.  If any of those methods succeed, it defines
     'HAVE_ALLOCA'.  Otherwise, it sets the output variable 'ALLOCA' to
     'alloca.o' and defines 'C_ALLOCA' (so programs can periodically
     call 'alloca(0)' to garbage collect).  This variable is separate
     from 'LIBOBJS' so multiple programs can share the value of 'ALLOCA'
     without needing to create an actual library, in case only some of
     them use the code in 'LIBOBJS'.

     This macro does not try to get 'alloca' from the System V R3
     'libPW' or the System V R4 'libucb' because those libraries contain
     some incompatible functions that cause trouble.  Some versions do
     not even contain 'alloca' or contain a buggy version.  If you still
     want to use their 'alloca', use 'ar' to extract 'alloca.o' from
     them instead of compiling 'alloca.c'.

     Source files that use 'alloca' should start with a piece of code
     like the following, to declare it properly.  In some versions of
     AIX, the declaration of 'alloca' must precede everything else
     except for comments and preprocessor directives.  The '#pragma'
     directive is indented so that pre-ANSI C compilers will ignore it,
     rather than choke on it.

          /* AIX requires this to be the first thing in the file.  */
          #ifndef __GNUC__
          # if HAVE_ALLOCA_H
          #  include <alloca.h>
          # else
          #  ifdef _AIX
           #pragma alloca
          #  else
          #   ifndef alloca /* predefined by HP cc +Olibcalls */
          char *alloca ();
          #   endif
          #  endif
          # endif
          #endif

 -- Macro: AC_FUNC_CHOWN
     If the 'chown' function is available and works (in particular, it
     should accept '-1' for 'uid' and 'gid'), define 'HAVE_CHOWN'.

 -- Macro: AC_FUNC_CLOSEDIR_VOID
     If the 'closedir' function does not return a meaningful value,
     define 'CLOSEDIR_VOID'.  Otherwise, callers ought to check its
     return value for an error indicator.

 -- Macro: AC_FUNC_ERROR_AT_LINE
     If the 'error_at_line' function is not found, require an
     'AC_LIBOBJ' replacement of 'error'.

 -- Macro: AC_FUNC_FNMATCH
     If the 'fnmatch' function is available and works (unlike the one on
     Solaris 2.4), define 'HAVE_FNMATCH'.

 -- Macro: AC_FUNC_FORK
     This macro checks for the 'fork' and 'vfork' functions.  If a
     working 'fork' is found, define 'HAVE_WORKING_FORK'.  This macro
     checks whether 'fork' is just a stub by trying to run it.

     If 'vfork.h' is found, define 'HAVE_VFORK_H'.  If a working 'vfork'
     is found, define 'HAVE_WORKING_VFORK'.  Otherwise, define 'vfork'
     to be 'fork' for backward compatibility with previous versions of
     'autoconf'.  This macro checks for several known errors in
     implementations of 'vfork' and considers the system to not have a
     working 'vfork' if it detects any of them.  It is not considered to
     be an implementation error if a child's invocation of 'signal'
     modifies the parent's signal handler, since child processes rarely
     change their signal handlers.

     Since this macro defines 'vfork' only for backward compatibility
     with previous versions of 'autoconf' you're encouraged to define it
     yourself in new code:
          #if !HAVE_WORKING_VFORK
          # define vfork fork
          #endif

 -- Macro: AC_FUNC_FSEEKO
     If the 'fseeko' function is available, define 'HAVE_FSEEKO'.
     Define '_LARGEFILE_SOURCE' if necessary.

 -- Macro: AC_FUNC_GETGROUPS
     If the 'getgroups' function is available and works (unlike on
     Ultrix 4.3, where 'getgroups (0, 0)' always fails), define
     'HAVE_GETGROUPS'.  Set 'GETGROUPS_LIBS' to any libraries needed to
     get that function.  This macro runs 'AC_TYPE_GETGROUPS'.

 -- Macro: AC_FUNC_GETLOADAVG
     Check how to get the system load averages.  If the system has the
     'getloadavg' function, define 'HAVE_GETLOADAVG', and set
     'GETLOADAVG_LIBS' to any libraries needed to get that function.
     Also add 'GETLOADAVG_LIBS' to 'LIBS'.

     Otherwise, require an 'AC_LIBOBJ' replacement ('getloadavg.c') of
     'getloadavg', and possibly define several other C preprocessor
     macros and output variables:

       1. Define 'C_GETLOADAVG'.

       2. Define 'SVR4', 'DGUX', 'UMAX', or 'UMAX4_3' if on those
          systems.

       3. If 'nlist.h' is found, define 'NLIST_STRUCT'.

       4. If 'struct nlist' has an 'n_un.n_name' member, define
          'HAVE_STRUCT_NLIST_N_UN_N_NAME'.  The obsolete symbol
          'NLIST_NAME_UNION' is still defined, but do not depend upon
          it.

       5. Programs may need to be installed setgid (or setuid) for
          'getloadavg' to work.  In this case, define
          'GETLOADAVG_PRIVILEGED', set the output variable 'NEED_SETGID'
          to 'true' (and otherwise to 'false'), and set 'KMEM_GROUP' to
          the name of the group that should own the installed program.

 -- Macro: AC_FUNC_GETMNTENT
     Check for 'getmntent' in the 'sun', 'seq', and 'gen' libraries, for
     Irix 4, PTX, and Unixware, respectively.  Then, if 'getmntent' is
     available, define 'HAVE_GETMNTENT'.

 -- Macro: AC_FUNC_GETPGRP
     If 'getpgrp' takes no argument (the POSIX.1 version), define
     'GETPGRP_VOID'.  Otherwise, it is the BSD version, which takes a
     process ID as an argument.  This macro does not check whether
     'getpgrp' exists at all; if you need to work in that situation,
     first call 'AC_CHECK_FUNC' for 'getpgrp'.

 -- Macro: AC_FUNC_LSTAT_FOLLOWS_SLASHED_SYMLINK
     If 'link' is a symbolic link, then 'lstat' should treat 'link/' the
     same as 'link/.'.  However, many older 'lstat' implementations
     incorrectly ignore trailing slashes.

     It is safe to assume that if 'lstat' incorrectly ignores trailing
     slashes, then other symbolic-link-aware functions like 'unlink' and
     'unlink' also incorrectly ignore trailing slashes.

     If 'lstat' behaves properly, define
     'LSTAT_FOLLOWS_SLASHED_SYMLINK', otherwise require an 'AC_LIBOBJ'
     replacement of 'lstat'.

 -- Macro: AC_FUNC_MALLOC
     If the 'malloc' works correctly ('malloc (0)' returns a valid
     pointer), define 'HAVE_MALLOC'.

 -- Macro: AC_FUNC_MEMCMP
     If the 'memcmp' function is not available, or does not work on
     8-bit data (like the one on SunOS 4.1.3), or fails when comparing
     16 bytes or more and with at least one buffer not starting on a
     4-byte boundary (such as the one on NeXT x86 OpenStep), require an
     'AC_LIBOBJ' replacement for 'memcmp'.

 -- Macro: AC_FUNC_MKTIME
     If the 'mktime' function is not available, or does not work
     correctly, require an 'AC_LIBOBJ' replacement for 'mktime'.

 -- Macro: AC_FUNC_MMAP
     If the 'mmap' function exists and works correctly, define
     'HAVE_MMAP'.  Only checks private fixed mapping of already-mapped
     memory.

 -- Macro: AC_FUNC_OBSTACK
     If the obstacks are found, define 'HAVE_OBSTACK', else require an
     'AC_LIBOBJ' replacement for 'obstack'.

 -- Macro: AC_FUNC_SELECT_ARGTYPES
     Determines the correct type to be passed for each of the 'select'
     function's arguments, and defines those types in
     'SELECT_TYPE_ARG1', 'SELECT_TYPE_ARG234', and 'SELECT_TYPE_ARG5'
     respectively.  'SELECT_TYPE_ARG1' defaults to 'int',
     'SELECT_TYPE_ARG234' defaults to 'int *', and 'SELECT_TYPE_ARG5'
     defaults to 'struct timeval *'.

 -- Macro: AC_FUNC_SETPGRP
     If 'setpgrp' takes no argument (the POSIX.1 version), define
     'SETPGRP_VOID'.  Otherwise, it is the BSD version, which takes two
     process IDs as arguments.  This macro does not check whether
     'setpgrp' exists at all; if you need to work in that situation,
     first call 'AC_CHECK_FUNC' for 'setpgrp'.

 -- Macro: AC_FUNC_STAT
 -- Macro: AC_FUNC_LSTAT
     Determine whether 'stat' or 'lstat' have the bug that it succeeds
     when given the zero-length file name argument.  The 'stat' and
     'lstat' from SunOS 4.1.4 and the Hurd (as of 1998-11-01) do this.

     If it does, then define 'HAVE_STAT_EMPTY_STRING_BUG' (or
     'HAVE_LSTAT_EMPTY_STRING_BUG') and ask for an 'AC_LIBOBJ'
     replacement of it.

 -- Macro: AC_FUNC_SETVBUF_REVERSED
     If 'setvbuf' takes the buffering type as its second argument and
     the buffer pointer as the third, instead of the other way around,
     define 'SETVBUF_REVERSED'.

 -- Macro: AC_FUNC_STRCOLL
     If the 'strcoll' function exists and works correctly, define
     'HAVE_STRCOLL'.  This does a bit more than
     'AC_CHECK_FUNCS(strcoll)', because some systems have incorrect
     definitions of 'strcoll' that should not be used.

 -- Macro: AC_FUNC_STRTOD
     If the 'strtod' function does not exist or doesn't work correctly,
     ask for an 'AC_LIBOBJ' replacement of 'strtod'.  In this case,
     because 'strtod.c' is likely to need 'pow', set the output variable
     'POW_LIB' to the extra library needed.

 -- Macro: AC_FUNC_STRERROR_R
     If 'strerror_r' is available, define 'HAVE_STRERROR_R'.  If its
     implementation correctly returns a 'char *', define
     'HAVE_WORKING_STRERROR_R'.  On at least DEC UNIX 4.0[A-D] and HP-UX
     B.10.20, 'strerror_r' returns 'int'.  Actually, this tests only
     whether it returns a scalar or an array, but that should be enough.
     This is used by the common 'error.c'.

 -- Macro: AC_FUNC_STRFTIME
     Check for 'strftime' in the 'intl' library, for SCO UNIX.  Then, if
     'strftime' is available, define 'HAVE_STRFTIME'.

 -- Macro: AC_FUNC_UTIME_NULL
     If 'utime(FILE, NULL)' sets FILE's timestamp to the present, define
     'HAVE_UTIME_NULL'.

 -- Macro: AC_FUNC_VPRINTF
     If 'vprintf' is found, define 'HAVE_VPRINTF'.  Otherwise, if
     '_doprnt' is found, define 'HAVE_DOPRNT'.  (If 'vprintf' is
     available, you may assume that 'vfprintf' and 'vsprintf' are also
     available.)


File: autoconf.info,  Node: Generic Functions,  Prev: Particular Functions,  Up: Library Functions

5.5.3 Generic Function Checks
-----------------------------

These macros are used to find functions not covered by the "particular"
test macros.  If the functions might be in libraries other than the
default C library, first call 'AC_CHECK_LIB' for those libraries.  If
you need to check the behavior of a function as well as find out whether
it is present, you have to write your own test for it (*note Writing
Tests::).

 -- Macro: AC_CHECK_FUNC (FUNCTION, [ACTION-IF-FOUND],
          [ACTION-IF-NOT-FOUND])
     If C function FUNCTION is available, run shell commands
     ACTION-IF-FOUND, otherwise ACTION-IF-NOT-FOUND.  If you just want
     to define a symbol if the function is available, consider using
     'AC_CHECK_FUNCS' instead.  This macro checks for functions with C
     linkage even when 'AC_LANG(C++)' has been called, since C is more
     standardized than C++.  (*note Language Choice::, for more
     information about selecting the language for checks.)

 -- Macro: AC_CHECK_FUNCS (FUNCTION..., [ACTION-IF-FOUND],
          [ACTION-IF-NOT-FOUND])
     For each FUNCTION in the whitespace-separated argument list, define
     'HAVE_FUNCTION' (in all capitals) if it is available.  If
     ACTION-IF-FOUND is given, it is additional shell code to execute
     when one of the functions is found.  You can give it a value of
     'break' to break out of the loop on the first match.  If
     ACTION-IF-NOT-FOUND is given, it is executed when one of the
     functions is not found.

   Autoconf follows a philosophy that was formed over the years by those
who have struggled for portability: isolate the portability issues in
specific files, and then program as if you were in a POSIX environment.
Some functions may be missing or unfixable, and your package must be
ready to replace them.

   Use the first three of the following macros to specify a function to
be replaced, and the last one ('AC_REPLACE_FUNCS') to check for and
replace the function if needed.

 -- Macro: AC_LIBOBJ (FUNCTION)
     Specify that 'FUNCTION.c' must be included in the executables to
     replace a missing or broken implementation of FUNCTION.

     Technically, it adds 'FUNCTION.$ac_objext' to the output variable
     'LIBOBJS' and calls 'AC_LIBSOURCE' for 'FUNCTION.c'.  You should
     not directly change 'LIBOBJS', since this is not traceable.

 -- Macro: AC_LIBSOURCE (FILE)
     Specify that FILE might be needed to compile the project.  If you
     need to know what files might be needed by a 'configure.ac', you
     should trace 'AC_LIBSOURCE'.  FILE must be a literal.

     This macro is called automatically from 'AC_LIBOBJ', but you must
     call it explicitly if you pass a shell variable to 'AC_LIBOBJ'.  In
     that case, since shell variables cannot be traced statically, you
     must pass to 'AC_LIBSOURCE' any possible files that the shell
     variable might cause 'AC_LIBOBJ' to need.  For example, if you want
     to pass a variable '$foo_or_bar' to 'AC_LIBOBJ' that holds either
     '"foo"' or '"bar"', you should do:

          AC_LIBSOURCE(foo.c)
          AC_LIBSOURCE(bar.c)
          AC_LIBOBJ($foo_or_bar)

     There is usually a way to avoid this, however, and you are
     encouraged to simply call 'AC_LIBOBJ' with literal arguments.

     Note that this macro replaces the obsolete 'AC_LIBOBJ_DECL', with
     slightly different semantics: the old macro took the function name,
     e.g.  'foo', as its argument rather than the file name.

 -- Macro: AC_LIBSOURCES (FILES)
     Like 'AC_LIBSOURCE', but accepts one or more FILES in a
     comma-separated M4 list.  Thus, the above example might be
     rewritten:

          AC_LIBSOURCES([foo.c, bar.c])
          AC_LIBOBJ($foo_or_bar)

 -- Macro: AC_REPLACE_FUNCS (FUNCTION...)
     Like 'AC_CHECK_FUNCS', but uses 'AC_LIBOBJ(FUNCTION)' as
     ACTION-IF-NOT-FOUND.  You can declare your replacement function by
     enclosing the prototype in '#if !HAVE_FUNCTION'.  If the system has
     the function, it probably declares it in a header file you should
     be including, so you shouldn't redeclare it lest your declaration
     conflict.


File: autoconf.info,  Node: Header Files,  Next: Declarations,  Prev: Library Functions,  Up: Existing Tests

5.6 Header Files
================

The following macros check for the presence of certain C header files.
If there is no macro specifically defined to check for a header file you
need, and you don't need to check for any special properties of it, then
you can use one of the general header-file check macros.

* Menu:

* Particular Headers::          Special handling to find certain headers
* Generic Headers::             How to find other headers


File: autoconf.info,  Node: Particular Headers,  Next: Generic Headers,  Prev: Header Files,  Up: Header Files

5.6.1 Particular Header Checks
------------------------------

These macros check for particular system header files--whether they
exist, and in some cases whether they declare certain symbols.

 -- Macro: AC_HEADER_DIRENT
     Check for the following header files.  For the first one that is
     found and defines 'DIR', define the listed C preprocessor macro:

     'dirent.h'     'HAVE_DIRENT_H'
     'sys/ndir.h'   'HAVE_SYS_NDIR_H'
     'sys/dir.h'    'HAVE_SYS_DIR_H'
     'ndir.h'       'HAVE_NDIR_H'

     The directory-library declarations in your source code should look
     something like the following:

          #if HAVE_DIRENT_H
          # include <dirent.h>
          # define NAMLEN(dirent) strlen((dirent)->d_name)
          #else
          # define dirent direct
          # define NAMLEN(dirent) (dirent)->d_namlen
          # if HAVE_SYS_NDIR_H
          #  include <sys/ndir.h>
          # endif
          # if HAVE_SYS_DIR_H
          #  include <sys/dir.h>
          # endif
          # if HAVE_NDIR_H
          #  include <ndir.h>
          # endif
          #endif

     Using the above declarations, the program would declare variables
     to be of type 'struct dirent', not 'struct direct', and would
     access the length of a directory entry name by passing a pointer to
     a 'struct dirent' to the 'NAMLEN' macro.

     This macro also checks for the SCO Xenix 'dir' and 'x' libraries.

 -- Macro: AC_HEADER_MAJOR
     If 'sys/types.h' does not define 'major', 'minor', and 'makedev',
     but 'sys/mkdev.h' does, define 'MAJOR_IN_MKDEV'; otherwise, if
     'sys/sysmacros.h' does, define 'MAJOR_IN_SYSMACROS'.

 -- Macro: AC_HEADER_STAT
     If the macros 'S_ISDIR', 'S_ISREG' et al.  defined in 'sys/stat.h'
     do not work properly (returning false positives), define
     'STAT_MACROS_BROKEN'.  This is the case on Tektronix UTekV, Amdahl
     UTS and Motorola System V/88.

 -- Macro: AC_HEADER_STDC
     Define 'STDC_HEADERS' if the system has ANSI C header files.
     Specifically, this macro checks for 'stdlib.h', 'stdarg.h',
     'string.h', and 'float.h'; if the system has those, it probably has
     the rest of the ANSI C header files.  This macro also checks
     whether 'string.h' declares 'memchr' (and thus presumably the other
     'mem' functions), whether 'stdlib.h' declare 'free' (and thus
     presumably 'malloc' and other related functions), and whether the
     'ctype.h' macros work on characters with the high bit set, as ANSI
     C requires.

     Use 'STDC_HEADERS' instead of '__STDC__' to determine whether the
     system has ANSI-compliant header files (and probably C library
     functions) because many systems that have GCC do not have ANSI C
     header files.

     On systems without ANSI C headers, there is so much variation that
     it is probably easier to declare the functions you use than to
     figure out exactly what the system header files declare.  Some
     systems contain a mix of functions ANSI and BSD; some are mostly
     ANSI but lack 'memmove'; some define the BSD functions as macros in
     'string.h' or 'strings.h'; some have only the BSD functions but
     'string.h'; some declare the memory functions in 'memory.h', some
     in 'string.h'; etc.  It is probably sufficient to check for one
     string function and one memory function; if the library has the
     ANSI versions of those then it probably has most of the others.  If
     you put the following in 'configure.ac':

          AC_HEADER_STDC
          AC_CHECK_FUNCS(strchr memcpy)

     then, in your code, you can put declarations like this:

          #if STDC_HEADERS
          # include <string.h>
          #else
          # if !HAVE_STRCHR
          #  define strchr index
          #  define strrchr rindex
          # endif
          char *strchr (), *strrchr ();
          # if !HAVE_MEMCPY
          #  define memcpy(d, s, n) bcopy ((s), (d), (n))
          #  define memmove(d, s, n) bcopy ((s), (d), (n))
          # endif
          #endif

     If you use a function like 'memchr', 'memset', 'strtok', or
     'strspn', which have no BSD equivalent, then macros won't suffice;
     you must provide an implementation of each function.  An easy way
     to incorporate your implementations only when needed (since the
     ones in system C libraries may be hand optimized) is to, taking
     'memchr' for example, put it in 'memchr.c' and use
     'AC_REPLACE_FUNCS(memchr)'.

 -- Macro: AC_HEADER_SYS_WAIT
     If 'sys/wait.h' exists and is compatible with POSIX.1, define
     'HAVE_SYS_WAIT_H'.  Incompatibility can occur if 'sys/wait.h' does
     not exist, or if it uses the old BSD 'union wait' instead of 'int'
     to store a status value.  If 'sys/wait.h' is not POSIX.1
     compatible, then instead of including it, define the POSIX.1 macros
     with their usual interpretations.  Here is an example:

          #include <sys/types.h>
          #if HAVE_SYS_WAIT_H
          # include <sys/wait.h>
          #endif
          #ifndef WEXITSTATUS
          # define WEXITSTATUS(stat_val) ((unsigned)(stat_val) >> 8)
          #endif
          #ifndef WIFEXITED
          # define WIFEXITED(stat_val) (((stat_val) & 255) == 0)
          #endif

   '_POSIX_VERSION' is defined when 'unistd.h' is included on POSIX.1
systems.  If there is no 'unistd.h', it is definitely not a POSIX.1
system.  However, some non-POSIX.1 systems do have 'unistd.h'.

   The way to check if the system supports POSIX.1 is:

     #if HAVE_UNISTD_H
     # include <sys/types.h>
     # include <unistd.h>
     #endif

     #ifdef _POSIX_VERSION
     /* Code for POSIX.1 systems.  */
     #endif

 -- Macro: AC_HEADER_TIME
     If a program may include both 'time.h' and 'sys/time.h', define
     'TIME_WITH_SYS_TIME'.  On some older systems, 'sys/time.h' includes
     'time.h', but 'time.h' is not protected against multiple inclusion,
     so programs should not explicitly include both files.  This macro
     is useful in programs that use, for example, 'struct timeval' or
     'struct timezone' as well as 'struct tm'.  It is best used in
     conjunction with 'HAVE_SYS_TIME_H', which can be checked for using
     'AC_CHECK_HEADERS(sys/time.h)'.

          #if TIME_WITH_SYS_TIME
          # include <sys/time.h>
          # include <time.h>
          #else
          # if HAVE_SYS_TIME_H
          #  include <sys/time.h>
          # else
          #  include <time.h>
          # endif
          #endif

 -- Macro: AC_HEADER_TIOCGWINSZ
     If the use of 'TIOCGWINSZ' requires '<sys/ioctl.h>', then define
     'GWINSZ_IN_SYS_IOCTL'.  Otherwise 'TIOCGWINSZ' can be found in
     '<termios.h>'.

     Use:

          #if HAVE_TERMIOS_H
          # include <termios.h>
          #endif

          #if GWINSZ_IN_SYS_IOCTL
          # include <sys/ioctl.h>
          #endif


File: autoconf.info,  Node: Generic Headers,  Prev: Particular Headers,  Up: Header Files

5.6.2 Generic Header Checks
---------------------------

These macros are used to find system header files not covered by the
"particular" test macros.  If you need to check the contents of a header
as well as find out whether it is present, you have to write your own
test for it (*note Writing Tests::).

 -- Macro: AC_CHECK_HEADER (HEADER-FILE, [ACTION-IF-FOUND],
          [ACTION-IF-NOT-FOUND], [INCLUDES])
     If the system header file HEADER-FILE is usable, execute shell
     commands ACTION-IF-FOUND, otherwise execute ACTION-IF-NOT-FOUND.
     If you just want to define a symbol if the header file is
     available, consider using 'AC_CHECK_HEADERS' instead.

     The meaning of "usable" depends upon the content of INCLUDES:

     if INCLUDES is empty
          check whether

               HEADER-FILE

          can be _preprocessed_ without error.

     if INCLUDE is set
          Check whether

               INCLUDES
               #include <HEADER-FILE>

          can be _compiled_ without error.  You may use
          'AC_CHECK_HEADER' (and 'AC_CHECK_HEADERS') to check whether
          two headers are compatible.

     You may pass any kind of dummy content for INCLUDES, such as a
     single space, a comment, to check whether HEADER-FILE compiles with
     success.

 -- Macro: AC_CHECK_HEADERS (HEADER-FILE..., [ACTION-IF-FOUND],
          [ACTION-IF-NOT-FOUND], [INCLUDES])
     For each given system header file HEADER-FILE in the
     whitespace-separated argument list that exists, define
     'HAVE_HEADER-FILE' (in all capitals).  If ACTION-IF-FOUND is given,
     it is additional shell code to execute when one of the header files
     is found.  You can give it a value of 'break' to break out of the
     loop on the first match.  If ACTION-IF-NOT-FOUND is given, it is
     executed when one of the header files is not found.

     Be sure to read the documentation of 'AC_CHECK_HEADER' to
     understand the influence of INCLUDES.


File: autoconf.info,  Node: Declarations,  Next: Structures,  Prev: Header Files,  Up: Existing Tests

5.7 Declarations
================

The following macros check for the declaration of variables and
functions.  If there is no macro specifically defined to check for a
symbol you need, then you can use the general macros (*note Generic
Declarations::) or, for more complex tests, you may use 'AC_TRY_COMPILE'
(*note Examining Syntax::).

* Menu:

* Particular Declarations::     Macros to check for certain declarations
* Generic Declarations::        How to find other declarations


File: autoconf.info,  Node: Particular Declarations,  Next: Generic Declarations,  Prev: Declarations,  Up: Declarations

5.7.1 Particular Declaration Checks
-----------------------------------

The following macros check for certain declarations.

 -- Macro: AC_DECL_SYS_SIGLIST
     Define 'SYS_SIGLIST_DECLARED' if the variable 'sys_siglist' is
     declared in a system header file, either 'signal.h' or 'unistd.h'.


File: autoconf.info,  Node: Generic Declarations,  Prev: Particular Declarations,  Up: Declarations

5.7.2 Generic Declaration Checks
--------------------------------

These macros are used to find declarations not covered by the
"particular" test macros.

 -- Macro: AC_CHECK_DECL (SYMBOL, [ACTION-IF-FOUND],
          [ACTION-IF-NOT-FOUND], [INCLUDES])
     If SYMBOL (a function or a variable) is not declared in INCLUDES
     and a declaration is needed, run the shell commands
     ACTION-IF-NOT-FOUND, otherwise ACTION-IF-FOUND.  If no INCLUDES are
     specified, the default includes are used (*note Default
     Includes::).

     This macro actually tests whether it is valid to use SYMBOL as an
     r-value, not if it is really declared, because it is much safer to
     avoid introducing extra declarations when they are not needed.

 -- Macro: AC_CHECK_DECLS (SYMBOLS, [ACTION-IF-FOUND],
          [ACTION-IF-NOT-FOUND], [INCLUDES])
     For each of the SYMBOLS (_comma_-separated list), define
     'HAVE_DECL_SYMBOL' (in all capitals) to '1' if SYMBOL is declared,
     otherwise to '0'.  If ACTION-IF-NOT-FOUND is given, it is
     additional shell code to execute when one of the function
     declarations is needed, otherwise ACTION-IF-FOUND is executed.

     This macro uses an m4 list as first argument:
          AC_CHECK_DECLS(strdup)
          AC_CHECK_DECLS([strlen])
          AC_CHECK_DECLS([malloc, realloc, calloc, free])

     Unlike the other 'AC_CHECK_*S' macros, when a SYMBOL is not
     declared, 'HAVE_DECL_SYMBOL' is defined to '0' instead of leaving
     'HAVE_DECL_SYMBOL' undeclared.  When you are _sure_ that the check
     was performed, use 'HAVE_DECL_SYMBOL' just like any other result of
     Autoconf:

          #if !HAVE_DECL_SYMBOL
          extern char *symbol;
          #endif

     If the test may have not been performed, however, because it is
     safer _not_ to declare a symbol than to use a declaration that
     conflicts with the system's one, you should use:

          #if defined HAVE_DECL_MALLOC && !HAVE_DECL_MALLOC
          char *malloc (size_t *s);
          #endif

     You fall into the second category only in extreme situations:
     either your files may be used without being configured, or they are
     used during the configuration.  In most cases the traditional
     approach is enough.


File: autoconf.info,  Node: Structures,  Next: Types,  Prev: Declarations,  Up: Existing Tests

5.8 Structures
==============

The following macros check for the presence of certain members in C
structures.  If there is no macro specifically defined to check for a
member you need, then you can use the general structure-member macro
(*note Generic Structures::) or, for more complex tests, you may use
'AC_TRY_COMPILE' (*note Examining Syntax::).

* Menu:

* Particular Structures::       Macros to check for certain structure members
* Generic Structures::          How to find other structure members


File: autoconf.info,  Node: Particular Structures,  Next: Generic Structures,  Prev: Structures,  Up: Structures

5.8.1 Particular Structure Checks
---------------------------------

The following macros check for certain structures or structure members.

 -- Macro: AC_STRUCT_ST_BLKSIZE
     If 'struct stat' contains an 'st_blksize' member, define
     'HAVE_STRUCT_STAT_ST_BLKSIZE'.  The former name, 'HAVE_ST_BLKSIZE'
     is to be avoided, as its support will cease in the future.  This
     macro is obsoleted, and should be replaced by

          AC_CHECK_MEMBERS([struct stat.st_blksize])

 -- Macro: AC_STRUCT_ST_BLOCKS
     If 'struct stat' contains an 'st_blocks' member, define
     'HAVE_STRUCT STAT_ST_BLOCKS'.  Otherwise, require an 'AC_LIBOBJ'
     replacement of 'fileblocks'.  The former name, 'HAVE_ST_BLOCKS' is
     to be avoided, as its support will cease in the future.

 -- Macro: AC_STRUCT_ST_RDEV
     If 'struct stat' contains an 'st_rdev' member, define
     'HAVE_STRUCT_STAT_ST_RDEV'.  The former name for this macro,
     'HAVE_ST_RDEV', is to be avoided as it will cease to be supported
     in the future.  Actually, even the new macro is obsolete, and
     should be replaced by:
          AC_CHECK_MEMBERS([struct stat.st_rdev])

 -- Macro: AC_STRUCT_TM
     If 'time.h' does not define 'struct tm', define 'TM_IN_SYS_TIME',
     which means that including 'sys/time.h' had better define 'struct
     tm'.

 -- Macro: AC_STRUCT_TIMEZONE
     Figure out how to get the current timezone.  If 'struct tm' has a
     'tm_zone' member, define 'HAVE_STRUCT_TM_TM_ZONE' (and the
     obsoleted 'HAVE_TM_ZONE').  Otherwise, if the external array
     'tzname' is found, define 'HAVE_TZNAME'.


File: autoconf.info,  Node: Generic Structures,  Prev: Particular Structures,  Up: Structures

5.8.2 Generic Structure Checks
------------------------------

These macros are used to find structure members not covered by the
"particular" test macros.

 -- Macro: AC_CHECK_MEMBER (AGGREGATE.MEMBER, [ACTION-IF-FOUND],
          [ACTION-IF-NOT-FOUND], [INCLUDES])
     Check whether MEMBER is a member of the aggregate AGGREGATE.  If no
     INCLUDES are specified, the default includes are used (*note
     Default Includes::).

          AC_CHECK_MEMBER(struct passwd.pw_gecos,,
                          [AC_MSG_ERROR([We need `passwd.pw_gecos'!])],
                          [#include <pwd.h>])

     You can use this macro for sub-members:

          AC_CHECK_MEMBER(struct top.middle.bot)

 -- Macro: AC_CHECK_MEMBERS (MEMBERS, [ACTION-IF-FOUND],
          [ACTION-IF-NOT-FOUND], [INCLUDES])
     Check for the existence of each 'AGGREGATE.MEMBER' of MEMBERS using
     the previous macro.  When MEMBER belongs to AGGREGATE, define
     'HAVE_AGGREGATE_MEMBER' (in all capitals, with spaces and dots
     replaced by underscores).

     This macro uses m4 lists:
          AC_CHECK_MEMBERS([struct stat.st_rdev, struct stat.st_blksize])


File: autoconf.info,  Node: Types,  Next: Compilers and Preprocessors,  Prev: Structures,  Up: Existing Tests

5.9 Types
=========

The following macros check for C types, either builtin or typedefs.  If
there is no macro specifically defined to check for a type you need, and
you don't need to check for any special properties of it, then you can
use a general type-check macro.

* Menu:

* Particular Types::            Special handling to find certain types
* Generic Types::               How to find other types


File: autoconf.info,  Node: Particular Types,  Next: Generic Types,  Prev: Types,  Up: Types

5.9.1 Particular Type Checks
----------------------------

These macros check for particular C types in 'sys/types.h', 'stdlib.h'
and others, if they exist.

 -- Macro: AC_TYPE_GETGROUPS
     Define 'GETGROUPS_T' to be whichever of 'gid_t' or 'int' is the
     base type of the array argument to 'getgroups'.

 -- Macro: AC_TYPE_MODE_T
     Equivalent to 'AC_CHECK_TYPE(mode_t, int)'.

 -- Macro: AC_TYPE_OFF_T
     Equivalent to 'AC_CHECK_TYPE(off_t, long)'.

 -- Macro: AC_TYPE_PID_T
     Equivalent to 'AC_CHECK_TYPE(pid_t, int)'.

 -- Macro: AC_TYPE_SIGNAL
     If 'signal.h' declares 'signal' as returning a pointer to a
     function returning 'void', define 'RETSIGTYPE' to be 'void';
     otherwise, define it to be 'int'.

     Define signal handlers as returning type 'RETSIGTYPE':

          RETSIGTYPE
          hup_handler ()
          {
          ...
          }

 -- Macro: AC_TYPE_SIZE_T
     Equivalent to 'AC_CHECK_TYPE(size_t, unsigned)'.

 -- Macro: AC_TYPE_UID_T
     If 'uid_t' is not defined, define 'uid_t' to be 'int' and 'gid_t'
     to be 'int'.


File: autoconf.info,  Node: Generic Types,  Prev: Particular Types,  Up: Types

5.9.2 Generic Type Checks
-------------------------

These macros are used to check for types not covered by the "particular"
test macros.

 -- Macro: AC_CHECK_TYPE (TYPE, [ACTION-IF-FOUND],
          [ACTION-IF-NOT-FOUND], [INCLUDES])
     Check whether TYPE is defined.  It may be a compiler builtin type
     or defined by the [INCLUDES] (*note Default Includes::).

 -- Macro: AC_CHECK_TYPES (TYPES, [ACTION-IF-FOUND],
          [ACTION-IF-NOT-FOUND], [INCLUDES])
     For each TYPE of the TYPES that is defined, define 'HAVE_TYPE' (in
     all capitals).  If no INCLUDES are specified, the default includes
     are used (*note Default Includes::).  If ACTION-IF-FOUND is given,
     it is additional shell code to execute when one of the types is
     found.  If ACTION-IF-NOT-FOUND is given, it is executed when one of
     the types is not found.

     This macro uses m4 lists:
          AC_CHECK_TYPES(ptrdiff_t)
          AC_CHECK_TYPES([unsigned long long, uintmax_t])

   Autoconf, up to 2.13, used to provide to another version of
'AC_CHECK_TYPE', broken by design.  In order to keep backward
compatibility, a simple heuristics, quite safe but not totally, is
implemented.  In case of doubt, read the documentation of the former
'AC_CHECK_TYPE', see *note Obsolete Macros::.


File: autoconf.info,  Node: Compilers and Preprocessors,  Next: System Services,  Prev: Types,  Up: Existing Tests

5.10 Compilers and Preprocessors
================================

All the tests for compilers ('AC_PROG_CC', 'AC_PROG_CXX', 'AC_PROG_F77')
define the output variable 'EXEEXT' based on the output of the compiler,
typically to the empty string if Unix and '.exe' if Win32 or OS/2.

   They also define the output variable 'OBJEXT' based on the output of
the compiler, after .c files have been excluded, typically to 'o' if
Unix, 'obj' if Win32.

   If the compiler being used does not produce executables, they fail.
If the executables can't be run, and cross-compilation is not enabled,
they fail too.  *Note Manual Configuration::, for more on support for
cross compiling.

* Menu:

* Generic Compiler Characteristics::  Language independent tests
* C Compiler::                  Checking its characteristics
* C++ Compiler::                Likewise
* Fortran 77 Compiler::         Likewise


File: autoconf.info,  Node: Generic Compiler Characteristics,  Next: C Compiler,  Prev: Compilers and Preprocessors,  Up: Compilers and Preprocessors

5.10.1 Generic Compiler Characteristics
---------------------------------------

 -- Macro: AC_CHECK_SIZEOF (TYPE, [UNUSED], [INCLUDES])
     Define 'SIZEOF_TYPE' (*note Standard Symbols::) to be the size in
     bytes of TYPE.  If 'type' is unknown, it gets a size of 0.  If no
     INCLUDES are specified, the default includes are used (*note
     Default Includes::).  If you provide INCLUDE, make sure to include
     'stdio.h' which is required for this macro to run.

     This macro now works even when cross-compiling.  The UNUSED
     argument was used when cross-compiling.

     For example, the call

          AC_CHECK_SIZEOF(int *)

     defines 'SIZEOF_INT_P' to be 8 on DEC Alpha AXP systems.


File: autoconf.info,  Node: C Compiler,  Next: C++ Compiler,  Prev: Generic Compiler Characteristics,  Up: Compilers and Preprocessors

5.10.2 C Compiler Characteristics
---------------------------------

 -- Macro: AC_PROG_CC ([COMPILER-SEARCH-LIST])
     Determine a C compiler to use.  If 'CC' is not already set in the
     environment, check for 'gcc' and 'cc', then for other C compilers.
     Set output variable 'CC' to the name of the compiler found.

     This macro may, however, be invoked with an optional first argument
     which, if specified, must be a space separated list of C compilers
     to search for.  This just gives the user an opportunity to specify
     an alternative search list for the C compiler.  For example, if you
     didn't like the default order, then you could invoke 'AC_PROG_CC'
     like this:

          AC_PROG_CC(cl egcs gcc cc)

     If using the GNU C compiler, set shell variable 'GCC' to 'yes'.  If
     output variable 'CFLAGS' was not already set, set it to '-g -O2'
     for the GNU C compiler ('-O2' on systems where GCC does not accept
     '-g'), or '-g' for other compilers.

 -- Macro: AC_PROG_CC_C_O
     If the C compiler does not accept the '-c' and '-o' options
     simultaneously, define 'NO_MINUS_C_MINUS_O'.  This macro actually
     tests both the compiler found by 'AC_PROG_CC', and, if different,
     the first 'cc' in the path.  The test fails if one fails.  This
     macro was created for GNU Make to choose the default C compilation
     rule.

 -- Macro: AC_PROG_CC_STDC
     If the C compiler is not in ANSI C mode by default, try to add an
     option to output variable 'CC' to make it so.  This macro tries
     various options that select ANSI C on some system or another.  It
     considers the compiler to be in ANSI C mode if it handles function
     prototypes correctly.

     If you use this macro, you should check after calling it whether
     the C compiler has been set to accept ANSI C; if not, the shell
     variable 'ac_cv_prog_cc_stdc' is set to 'no'.  If you wrote your
     source code in ANSI C, you can make an un-ANSIfied copy of it by
     using the program 'ansi2knr', which comes with Automake.

 -- Macro: AC_PROG_CPP
     Set output variable 'CPP' to a command that runs the C
     preprocessor.  If '$CC -E' doesn't work, '/lib/cpp' is used.  It is
     only portable to run 'CPP' on files with a '.c' extension.

     If the current language is C (*note Language Choice::), many of the
     specific test macros use the value of 'CPP' indirectly by calling
     'AC_TRY_CPP', 'AC_CHECK_HEADER', 'AC_EGREP_HEADER', or
     'AC_EGREP_CPP'.

     Some preprocessors don't indicate missing include files by the
     error status.  For such preprocessors an internal variable is set
     that causes other macros to check the standard error from the
     preprocessor and consider the test failed if any warnings have been
     reported.

   The following macros check for C compiler or machine architecture
features.  To check for characteristics not listed here, use
'AC_TRY_COMPILE' (*note Examining Syntax::) or 'AC_TRY_RUN' (*note Run
Time::)

 -- Macro: AC_C_BIGENDIAN
     If words are stored with the most significant byte first (like
     Motorola and SPARC, but not Intel and VAX, CPUs), define
     'WORDS_BIGENDIAN'.

 -- Macro: AC_C_CONST
     If the C compiler does not fully support the ANSI C qualifier
     'const', define 'const' to be empty.  Some C compilers that do not
     define '__STDC__' do support 'const'; some compilers that define
     '__STDC__' do not completely support 'const'.  Programs can simply
     use 'const' as if every C compiler supported it; for those that
     don't, the 'Makefile' or configuration header file will define it
     as empty.

     Occasionally installers use a C++ compiler to compile C code,
     typically because they lack a C compiler.  This causes problems
     with 'const', because C and C++ treat 'const' differently.  For
     example:

          const int foo;

     is valid in C but not in C++.  These differences unfortunately
     cannot be papered over by defining 'const' to be empty.

     If 'autoconf' detects this situation, it leaves 'const' alone, as
     this generally yields better results in practice.  However, using a
     C++ compiler to compile C code is not recommended or supported, and
     installers who run into trouble in this area should get a C
     compiler like GCC to compile their C code.

 -- Macro: AC_C_VOLATILE
     If the C compiler does not understand the keyword 'volatile',
     define 'volatile' to be empty.  Programs can simply use 'volatile'
     as if every C compiler supported it; for those that do not, the
     'Makefile' or configuration header will define it as empty.

     If the correctness of your program depends on the semantics of
     'volatile', simply defining it to be empty does, in a sense, break
     your code.  However, given that the compiler does not support
     'volatile', you are at its mercy anyway.  At least your program
     will compile, when it wouldn't before.

     In general, the 'volatile' keyword is a feature of ANSI C, so you
     might expect that 'volatile' is available only when '__STDC__' is
     defined.  However, Ultrix 4.3's native compiler does support
     volatile, but does not defined '__STDC__'.

 -- Macro: AC_C_INLINE
     If the C compiler supports the keyword 'inline', do nothing.
     Otherwise define 'inline' to '__inline__' or '__inline' if it
     accepts one of those, otherwise define 'inline' to be empty.

 -- Macro: AC_C_CHAR_UNSIGNED
     If the C type 'char' is unsigned, define '__CHAR_UNSIGNED__',
     unless the C compiler predefines it.

 -- Macro: AC_C_LONG_DOUBLE
     If the C compiler supports the 'long double' type, define
     'HAVE_LONG_DOUBLE'.  Some C compilers that do not define '__STDC__'
     do support the 'long double' type; some compilers that define
     '__STDC__' do not support 'long double'.

 -- Macro: AC_C_STRINGIZE
     If the C preprocessor supports the stringizing operator, define
     'HAVE_STRINGIZE'.  The stringizing operator is '#' and is found in
     macros such as this:

          #define x(y) #y

 -- Macro: AC_C_PROTOTYPES
     Check to see if function prototypes are understood by the compiler.
     If so, define 'PROTOTYPES'.  In the case the compiler does not
     handle prototypes, you should use 'ansi2knr', which comes with the
     Automake distribution, to unprotoize function definitions.  For
     function prototypes, you should first define 'PARAMS':

          #ifndef PARAMS
          # if PROTOTYPES
          #  define PARAMS(protos) protos
          # else /* no PROTOTYPES */
          #  define PARAMS(protos) ()
          # endif /* no PROTOTYPES */
          #endif

     then use it this way:

          size_t my_strlen PARAMS ((const char *));

 -- Macro: AC_PROG_GCC_TRADITIONAL
     Add '-traditional' to output variable 'CC' if using the GNU C
     compiler and 'ioctl' does not work properly without '-traditional'.
     That usually happens when the fixed header files have not been
     installed on an old system.  Since recent versions of the GNU C
     compiler fix the header files automatically when installed, this is
     becoming a less prevalent problem.


File: autoconf.info,  Node: C++ Compiler,  Next: Fortran 77 Compiler,  Prev: C Compiler,  Up: Compilers and Preprocessors

5.10.3 C++ Compiler Characteristics
-----------------------------------

 -- Macro: AC_PROG_CXX ([COMPILER-SEARCH-LIST])
     Determine a C++ compiler to use.  Check if the environment variable
     'CXX' or 'CCC' (in that order) is set; if so, then set output
     variable 'CXX' to its value.

     Otherwise, if the macro is invoked without an argument, then search
     for a C++ compiler under the likely names (first 'g++' and 'c++'
     then other names).  If none of those checks succeed, then as a last
     resort set 'CXX' to 'g++'.

     This macro may, however, be invoked with an optional first argument
     which, if specified, must be a space separated list of C++
     compilers to search for.  This just gives the user an opportunity
     to specify an alternative search list for the C++ compiler.  For
     example, if you didn't like the default order, then you could
     invoke 'AC_PROG_CXX' like this:

          AC_PROG_CXX(cl KCC CC cxx cc++ xlC aCC c++ g++ egcs gcc)

     If using the GNU C++ compiler, set shell variable 'GXX' to 'yes'.
     If output variable 'CXXFLAGS' was not already set, set it to '-g
     -O2' for the GNU C++ compiler ('-O2' on systems where G++ does not
     accept '-g'), or '-g' for other compilers.

 -- Macro: AC_PROG_CXXCPP
     Set output variable 'CXXCPP' to a command that runs the C++
     preprocessor.  If '$CXX -E' doesn't work, '/lib/cpp' is used.  It
     is only portable to run 'CXXCPP' on files with a '.c', '.C', or
     '.cc' extension.

     If the current language is C++ (*note Language Choice::), many of
     the specific test macros use the value of 'CXXCPP' indirectly by
     calling 'AC_TRY_CPP', 'AC_CHECK_HEADER', 'AC_EGREP_HEADER', or
     'AC_EGREP_CPP'.

     Some preprocessors don't indicate missing include files by the
     error status.  For such preprocessors an internal variable is set
     that causes other macros to check the standard error from the
     preprocessor and consider the test failed if any warnings have been
     reported.  However, it is not known whether such broken
     preprocessors exist for C++.


File: autoconf.info,  Node: Fortran 77 Compiler,  Prev: C++ Compiler,  Up: Compilers and Preprocessors

5.10.4 Fortran 77 Compiler Characteristics
------------------------------------------

 -- Macro: AC_PROG_F77 ([COMPILER-SEARCH-LIST])
     Determine a Fortran 77 compiler to use.  If 'F77' is not already
     set in the environment, then check for 'g77' and 'f77', and then
     some other names.  Set the output variable 'F77' to the name of the
     compiler found.

     This macro may, however, be invoked with an optional first argument
     which, if specified, must be a space separated list of Fortran 77
     compilers to search for.  This just gives the user an opportunity
     to specify an alternative search list for the Fortran 77 compiler.
     For example, if you didn't like the default order, then you could
     invoke 'AC_PROG_F77' like this:

          AC_PROG_F77(fl32 f77 fort77 xlf cf77 g77 f90 xlf90)

     If using 'g77' (the GNU Fortran 77 compiler), then 'AC_PROG_F77'
     will set the shell variable 'G77' to 'yes'.  If the output variable
     'FFLAGS' was not already set in the environment, then set it to '-g
     -02' for 'g77' (or '-O2' where 'g77' does not accept '-g').
     Otherwise, set 'FFLAGS' to '-g' for all other Fortran 77 compilers.

 -- Macro: AC_PROG_F77_C_O
     Test if the Fortran 77 compiler accepts the options '-c' and '-o'
     simultaneously, and define 'F77_NO_MINUS_C_MINUS_O' if it does not.

   The following macros check for Fortran 77 compiler characteristics.
To check for characteristics not listed here, use 'AC_TRY_COMPILE'
(*note Examining Syntax::) or 'AC_TRY_RUN' (*note Run Time::), making
sure to first set the current language to Fortran 77 'AC_LANG(Fortran
77)' (*note Language Choice::).

 -- Macro: AC_F77_LIBRARY_LDFLAGS
     Determine the linker flags (e.g.  '-L' and '-l') for the "Fortran
     77 intrinsic and run-time libraries" that are required to
     successfully link a Fortran 77 program or shared library.  The
     output variable 'FLIBS' is set to these flags.

     This macro is intended to be used in those situations when it is
     necessary to mix, e.g.  C++ and Fortran 77 source code into a
     single program or shared library (*note (automake)Mixing Fortran 77
     With C and C++::).

     For example, if object files from a C++ and Fortran 77 compiler
     must be linked together, then the C++ compiler/linker must be used
     for linking (since special C++-ish things need to happen at link
     time like calling global constructors, instantiating templates,
     enabling exception support, etc.).

     However, the Fortran 77 intrinsic and run-time libraries must be
     linked in as well, but the C++ compiler/linker doesn't know by
     default how to add these Fortran 77 libraries.  Hence, the macro
     'AC_F77_LIBRARY_LDFLAGS' was created to determine these Fortran 77
     libraries.

     The macro 'AC_F77_DUMMY_MAIN' or 'AC_F77_MAIN' will probably also
     be necessary to link C/C++ with Fortran; see below.

 -- Macro: AC_F77_DUMMY_MAIN ([ACTION-IF-FOUND], [ACTION-IF-NOT-FOUND])
     With many compilers, the Fortran libraries detected by
     'AC_F77_LIBRARY_LDFLAGS' provide their own 'main' entry function
     that initializes things like Fortran I/O, and which then calls a
     user-provided entry function named e.g.  'MAIN__' to run the user's
     program.  The 'AC_F77_DUMMY_MAIN' or 'AC_F77_MAIN' macro figures
     out how to deal with this interaction.

     When using Fortran for purely numerical functions (no I/O,
     etcetera), users often prefer to provide their own 'main' and skip
     the Fortran library initializations.  In this case, however, one
     may still need to provide a dummy 'MAIN__' routine in order to
     prevent linking errors on some systems.  'AC_F77_DUMMY_MAIN'
     detects whether any such routine is _required_ for linking, and
     what its name is; the shell variable 'F77_DUMMY_MAIN' holds this
     name, 'unknown' when no solution was found, and 'none' when no such
     dummy main is needed.

     By default, ACTION-IF-FOUND defines 'F77_DUMMY_MAIN' to the name of
     this routine (e.g.  'MAIN__') _if_ it is required.
     [ACTION-IF-NOT-FOUND] defaults to exiting with an error.

     In order to link with Fortran routines, the user's C/C++ program
     should then include the following code to define the dummy main if
     it is needed:

          #ifdef F77_DUMMY_MAIN
          #  ifdef __cplusplus
               extern "C"
          #  endif
             int F77_DUMMY_MAIN() { return 1; }
          #endif

     Note that 'AC_F77_DUMMY_MAIN' is called automatically from
     'AC_F77_WRAPPERS'; there is generally no need to call it explicitly
     unless one wants to change the default actions.

 -- Macro: AC_F77_MAIN
     As discussed above for 'AC_F77_DUMMY_MAIN', many Fortran libraries
     allow you to provide an entry point called e.g.  'MAIN__' instead
     of the usual 'main', which is then called by a 'main' function in
     the Fortran libraries that initializes things like Fortran I/O. The
     'AC_F77_MAIN' macro detects whether it is _possible_ to utilize
     such an alternate main function, and defines 'F77_MAIN' to the name
     of the function.  (If no alternate main function name is found,
     'F77_MAIN' is simply defined to 'main'.)

     Thus, when calling Fortran routines from C that perform things like
     I/O, one should use this macro and name the "main" function
     'F77_MAIN' instead of 'main'.

 -- Macro: AC_F77_WRAPPERS
     Defines C macros 'F77_FUNC(name,NAME)' and 'F77_FUNC_(name,NAME)'
     to properly mangle the names of C/C++ identifiers, and identifiers
     with underscores, respectively, so that they match the
     name-mangling scheme used by the Fortran 77 compiler.

     Fortran 77 is case-insensitive, and in order to achieve this the
     Fortran 77 compiler converts all identifiers into a canonical case
     and format.  To call a Fortran 77 subroutine from C or to write a C
     function that is callable from Fortran 77, the C program must
     explicitly use identifiers in the format expected by the Fortran 77
     compiler.  In order to do this, one simply wraps all C identifiers
     in one of the macros provided by 'AC_F77_WRAPPERS'.  For example,
     suppose you have the following Fortran 77 subroutine:

                subroutine foobar(x,y)
                double precision x, y
                y = 3.14159 * x
                return
                end

     You would then declare its prototype in C or C++ as:

          #define FOOBAR_F77 F77_FUNC(foobar,FOOBAR)
          #ifdef __cplusplus
          extern "C"  /* prevent C++ name mangling */
          #endif
          void FOOBAR_F77(double *x, double *y);

     Note that we pass both the lowercase and uppercase versions of the
     function name to 'F77_FUNC' so that it can select the right one.
     Note also that all parameters to Fortran 77 routines are passed as
     pointers (*note (automake)Mixing Fortran 77 With C and C++::).

     Although Autoconf tries to be intelligent about detecting the
     name-mangling scheme of the Fortran 77 compiler, there may be
     Fortran 77 compilers that it doesn't support yet.  In this case,
     the above code will generate a compile-time error, but some other
     behavior (e.g.  disabling Fortran-related features) can be induced
     by checking whether the 'F77_FUNC' macro is defined.

     Now, to call that routine from a C program, we would do something
     like:

          {
              double x = 2.7183, y;
              FOOBAR_F77(&x, &y);
          }

     If the Fortran 77 identifier contains an underscore (e.g.
     'foo_bar'), you should use 'F77_FUNC_' instead of 'F77_FUNC' (with
     the same arguments).  This is because some Fortran 77 compilers
     mangle names differently if they contain an underscore.

 -- Macro: AC_F77_FUNC (NAME, [SHELLVAR])
     Given an identifier NAME, set the shell variable SHELLVAR to hold
     the mangled version NAME according to the rules of the Fortran 77
     linker (see also 'AC_F77_WRAPPERS').  SHELLVAR is optional; if it
     is not supplied, the shell variable will be simply NAME.  The
     purpose of this macro is to give the caller a way to access the
     name-mangling information other than through the C preprocessor as
     above; for example, to call Fortran routines from some language
     other than C/C++.


File: autoconf.info,  Node: System Services,  Next: UNIX Variants,  Prev: Compilers and Preprocessors,  Up: Existing Tests

5.11 System Services
====================

The following macros check for operating system services or
capabilities.

 -- Macro: AC_PATH_X
     Try to locate the X Window System include files and libraries.  If
     the user gave the command line options '--x-includes=DIR' and
     '--x-libraries=DIR', use those directories.  If either or both were
     not given, get the missing values by running 'xmkmf' on a trivial
     'Imakefile' and examining the 'Makefile' that it produces.  If that
     fails (such as if 'xmkmf' is not present), look for them in several
     directories where they often reside.  If either method is
     successful, set the shell variables 'x_includes' and 'x_libraries'
     to their locations, unless they are in directories the compiler
     searches by default.

     If both methods fail, or the user gave the command line option
     '--without-x', set the shell variable 'no_x' to 'yes'; otherwise
     set it to the empty string.

 -- Macro: AC_PATH_XTRA
     An enhanced version of 'AC_PATH_X'.  It adds the C compiler flags
     that X needs to output variable 'X_CFLAGS', and the X linker flags
     to 'X_LIBS'.  Define 'X_DISPLAY_MISSING' if X is not available.

     This macro also checks for special libraries that some systems need
     in order to compile X programs.  It adds any that the system needs
     to output variable 'X_EXTRA_LIBS'.  And it checks for special X11R6
     libraries that need to be linked with before '-lX11', and adds any
     found to the output variable 'X_PRE_LIBS'.

 -- Macro: AC_SYS_INTERPRETER
     Check whether the system supports starting scripts with a line of
     the form '#! /bin/csh' to select the interpreter to use for the
     script.  After running this macro, shell code in 'configure.ac' can
     check the shell variable 'interpval'; it will be set to 'yes' if
     the system supports '#!', 'no' if not.

 -- Macro: AC_SYS_LARGEFILE
     Arrange for large-file support(1).  On some hosts, one must use
     special compiler options to build programs that can access large
     files.  Append any such options to the output variable 'CC'.
     Define '_FILE_OFFSET_BITS' and '_LARGE_FILES' if necessary.

     Large-file support can be disabled by configuring with the
     '--disable-largefile' option.

     If you use this macro, check that your program works even when
     'off_t' is longer than 'long', since this is common when large-file
     support is enabled.  For example, it is not correct to print an
     arbitrary 'off_t' value 'X' with 'printf ("%ld", (long) X)'.

 -- Macro: AC_SYS_LONG_FILE_NAMES
     If the system supports file names longer than 14 characters, define
     'HAVE_LONG_FILE_NAMES'.

 -- Macro: AC_SYS_POSIX_TERMIOS
     Check to see if POSIX termios headers and functions are available
     on the system.  If so, set the shell variable
     'am_cv_sys_posix_termios' to 'yes'.  If not, set the variable to
     'no'.

   ---------- Footnotes ----------

   (1) large-file support,
<http://www.sas.com/standards/large.file/x_open.20Mar96.html>.


File: autoconf.info,  Node: UNIX Variants,  Prev: System Services,  Up: Existing Tests

5.12 UNIX Variants
==================

The following macros check for certain operating systems that need
special treatment for some programs, due to exceptional oddities in
their header files or libraries.  These macros are warts; they will be
replaced by a more systematic approach, based on the functions they make
available or the environments they provide.

 -- Macro: AC_AIX
     If on AIX, define '_ALL_SOURCE'.  Allows the use of some BSD
     functions.  Should be called before any macros that run the C
     compiler.

 -- Macro: AC_ISC_POSIX
     If on a POSIXized ISC UNIX, define '_POSIX_SOURCE' and add '-posix'
     (for the GNU C compiler) or '-Xp' (for other C compilers) to output
     variable 'CC'.  This allows the use of POSIX facilities.  Must be
     called after 'AC_PROG_CC' and before any other macros that run the
     C compiler.

 -- Macro: AC_MINIX
     If on Minix, define '_MINIX' and '_POSIX_SOURCE' and define
     '_POSIX_1_SOURCE' to be 2.  This allows the use of POSIX
     facilities.  Should be called before any macros that run the C
     compiler.


File: autoconf.info,  Node: Writing Tests,  Next: Results,  Prev: Existing Tests,  Up: Top

6 Writing Tests
***************

If the existing feature tests don't do something you need, you have to
write new ones.  These macros are the building blocks.  They provide
ways for other macros to check whether various kinds of features are
available and report the results.

   This chapter contains some suggestions and some of the reasons why
the existing tests are written the way they are.  You can also learn a
lot about how to write Autoconf tests by looking at the existing ones.
If something goes wrong in one or more of the Autoconf tests, this
information can help you understand the assumptions behind them, which
might help you figure out how to best solve the problem.

   These macros check the output of the C compiler system.  They do not
cache the results of their tests for future use (*note Caching
Results::), because they don't know enough about the information they
are checking for to generate a cache variable name.  They also do not
print any messages, for the same reason.  The checks for particular
kinds of C features call these macros and do cache their results and
print messages about what they're checking for.

   When you write a feature test that could be applicable to more than
one software package, the best thing to do is encapsulate it in a new
macro.  *Note Writing Autoconf Macros::, for how to do that.

* Menu:

* Examining Declarations::      Detecting header files and declarations
* Examining Syntax::            Detecting language syntax features
* Examining Libraries::         Detecting functions and global variables
* Run Time::                    Testing for run-time features
* Systemology::                 A zoology of operating systems
* Multiple Cases::              Tests for several possible values
* Language Choice::             Selecting which language to use for testing


File: autoconf.info,  Node: Examining Declarations,  Next: Examining Syntax,  Prev: Writing Tests,  Up: Writing Tests

6.1 Examining Declarations
==========================

The macro 'AC_TRY_CPP' is used to check whether particular header files
exist.  You can check for one at a time, or more than one if you need
several header files to all exist for some purpose.

 -- Macro: AC_TRY_CPP (INCLUDES, [ACTION-IF-TRUE], [ACTION-IF-FALSE])
     INCLUDES is C or C++ '#include' statements and declarations, on
     which shell variable, back quote, and backslash substitutions are
     performed.  (Actually, it can be any C program, but other
     statements are probably not useful.)  If the preprocessor produces
     no error messages while processing it, run shell commands
     ACTION-IF-TRUE.  Otherwise run shell commands ACTION-IF-FALSE.

     This macro uses 'CPPFLAGS', but not 'CFLAGS', because '-g', '-O',
     etc.  are not valid options to many C preprocessors.

   Here is how to find out whether a header file contains a particular
declaration, such as a typedef, a structure, a structure member, or a
function.  Use 'AC_EGREP_HEADER' instead of running 'grep' directly on
the header file; on some systems the symbol might be defined in another
header file that the file you are checking '#include's.

 -- Macro: AC_EGREP_HEADER (PATTERN, HEADER-FILE, ACTION-IF-FOUND,
          [ACTION-IF-NOT-FOUND])
     If the output of running the preprocessor on the system header file
     HEADER-FILE matches the 'egrep' regular expression PATTERN, execute
     shell commands ACTION-IF-FOUND, otherwise execute
     ACTION-IF-NOT-FOUND.

   To check for C preprocessor symbols, either defined by header files
or predefined by the C preprocessor, use 'AC_EGREP_CPP'.  Here is an
example of the latter:

     AC_EGREP_CPP(yes,
     [#ifdef _AIX
       yes
     #endif
     ], is_aix=yes, is_aix=no)

 -- Macro: AC_EGREP_CPP (PATTERN, PROGRAM, [ACTION-IF-FOUND],
          [ACTION-IF-NOT-FOUND])
     PROGRAM is the text of a C or C++ program, on which shell variable,
     back quote, and backslash substitutions are performed.  If the
     output of running the preprocessor on PROGRAM matches the 'egrep'
     regular expression PATTERN, execute shell commands ACTION-IF-FOUND,
     otherwise execute ACTION-IF-NOT-FOUND.

     This macro calls 'AC_PROG_CPP' or 'AC_PROG_CXXCPP' (depending on
     which language is current, *note Language Choice::), if it hasn't
     been called already.


File: autoconf.info,  Node: Examining Syntax,  Next: Examining Libraries,  Prev: Examining Declarations,  Up: Writing Tests

6.2 Examining Syntax
====================

To check for a syntax feature of the C, C++ or Fortran 77 compiler, such
as whether it recognizes a certain keyword, use 'AC_TRY_COMPILE' to try
to compile a small program that uses that feature.  You can also use it
to check for structures and structure members that are not present on
all systems.

 -- Macro: AC_TRY_COMPILE (INCLUDES, FUNCTION-BODY, [ACTION-IF-FOUND],
          [ACTION-IF-NOT-FOUND])
     Create a C, C++ or Fortran 77 test program (depending on which
     language is current, *note Language Choice::), to see whether a
     function whose body consists of FUNCTION-BODY can be compiled.

     For C and C++, INCLUDES is any '#include' statements needed by the
     code in FUNCTION-BODY (INCLUDES will be ignored if the currently
     selected language is Fortran 77).  This macro also uses 'CFLAGS' or
     'CXXFLAGS' if either C or C++ is the currently selected language,
     as well as 'CPPFLAGS', when compiling.  If Fortran 77 is the
     currently selected language then 'FFLAGS' will be used when
     compiling.

     If the file compiles successfully, run shell commands
     ACTION-IF-FOUND, otherwise run ACTION-IF-NOT-FOUND.

     This macro does not try to link; use 'AC_TRY_LINK' if you need to
     do that (*note Examining Libraries::).


File: autoconf.info,  Node: Examining Libraries,  Next: Run Time,  Prev: Examining Syntax,  Up: Writing Tests

6.3 Examining Libraries
=======================

To check for a library, a function, or a global variable, Autoconf
'configure' scripts try to compile and link a small program that uses
it.  This is unlike Metaconfig, which by default uses 'nm' or 'ar' on
the C library to try to figure out which functions are available.
Trying to link with the function is usually a more reliable approach
because it avoids dealing with the variations in the options and output
formats of 'nm' and 'ar' and in the location of the standard libraries.
It also allows configuring for cross-compilation or checking a
function's runtime behavior if needed.  On the other hand, it can be
slower than scanning the libraries once.

   A few systems have linkers that do not return a failure exit status
when there are unresolved functions in the link.  This bug makes the
configuration scripts produced by Autoconf unusable on those systems.
However, some of them can be given options that make the exit status
correct.  This is a problem that Autoconf does not currently handle
automatically.  If users encounter this problem, they might be able to
solve it by setting 'LDFLAGS' in the environment to pass whatever
options the linker needs (for example, '-Wl,-dn' on MIPS RISC/OS).

   'AC_TRY_LINK' is used to compile test programs to test for functions
and global variables.  It is also used by 'AC_CHECK_LIB' to check for
libraries (*note Libraries::), by adding the library being checked for
to 'LIBS' temporarily and trying to link a small program.

 -- Macro: AC_TRY_LINK (INCLUDES, FUNCTION-BODY, [ACTION-IF-FOUND],
          [ACTION-IF-NOT-FOUND])
     Depending on the current language (*note Language Choice::), create
     a test program to see whether a function whose body consists of
     FUNCTION-BODY can be compiled and linked.

     For C and C++, INCLUDES is any '#include' statements needed by the
     code in FUNCTION-BODY (INCLUDES will be ignored if the currently
     selected language is Fortran 77).  This macro also uses 'CFLAGS' or
     'CXXFLAGS' if either C or C++ is the currently selected language,
     as well as 'CPPFLAGS', when compiling.  If Fortran 77 is the
     currently selected language then 'FFLAGS' will be used when
     compiling.  However, both 'LDFLAGS' and 'LIBS' will be used during
     linking in all cases.

     If the file compiles and links successfully, run shell commands
     ACTION-IF-FOUND, otherwise run ACTION-IF-NOT-FOUND.

 -- Macro: AC_TRY_LINK_FUNC (FUNCTION, [ACTION-IF-FOUND],
          [ACTION-IF-NOT-FOUND])
     Depending on the current language (*note Language Choice::), create
     a test program to see whether a program whose body consists of a
     prototype of and a call to FUNCTION can be compiled and linked.

     If the file compiles and links successfully, run shell commands
     ACTION-IF-FOUND, otherwise run ACTION-IF-NOT-FOUND.


File: autoconf.info,  Node: Run Time,  Next: Systemology,  Prev: Examining Libraries,  Up: Writing Tests

6.4 Checking Run Time Behavior
==============================

Sometimes you need to find out how a system performs at run time, such
as whether a given function has a certain capability or bug.  If you
can, make such checks when your program runs instead of when it is
configured.  You can check for things like the machine's endianness when
your program initializes itself.

   If you really need to test for a run-time behavior while configuring,
you can write a test program to determine the result, and compile and
run it using 'AC_TRY_RUN'.  Avoid running test programs if possible,
because this prevents people from configuring your package for
cross-compiling.

* Menu:

* Test Programs::               Running test programs
* Guidelines::                  General rules for writing test programs
* Test Functions::              Avoiding pitfalls in test programs


File: autoconf.info,  Node: Test Programs,  Next: Guidelines,  Prev: Run Time,  Up: Run Time

6.4.1 Running Test Programs
---------------------------

Use the following macro if you need to test run-time behavior of the
system while configuring.

 -- Macro: AC_TRY_RUN (PROGRAM, [ACTION-IF-TRUE], [ACTION-IF-FALSE],
          [ACTION-IF-CROSS-COMPILING])
     PROGRAM is the text of a C program, on which shell variable and
     back quote substitutions are performed.  If it compiles and links
     successfully and returns an exit status of 0 when executed, run
     shell commands ACTION-IF-TRUE.  Otherwise, run shell commands
     ACTION-IF-FALSE; the exit status of the program is available in the
     shell variable '$?'.  This macro uses 'CFLAGS' or 'CXXFLAGS',
     'CPPFLAGS', 'LDFLAGS', and 'LIBS' when compiling.

     If the C compiler being used does not produce executables that run
     on the system where 'configure' is being run, then the test program
     is not run.  If the optional shell commands
     ACTION-IF-CROSS-COMPILING are given, they are run instead.
     Otherwise, 'configure' prints an error message and exits.

   Try to provide a pessimistic default value to use when
cross-compiling makes run-time tests impossible.  You do this by passing
the optional last argument to 'AC_TRY_RUN'.  'autoconf' prints a warning
message when creating 'configure' each time it encounters a call to
'AC_TRY_RUN' with no ACTION-IF-CROSS-COMPILING argument given.  You may
ignore the warning, though users will not be able to configure your
package for cross-compiling.  A few of the macros distributed with
Autoconf produce this warning message.

   To configure for cross-compiling you can also choose a value for
those parameters based on the canonical system name (*note Manual
Configuration::).  Alternatively, set up a test results cache file with
the correct values for the host system (*note Caching Results::).

   To provide a default for calls of 'AC_TRY_RUN' that are embedded in
other macros, including a few of the ones that come with Autoconf, you
can call 'AC_PROG_CC' before running them.  Then, if the shell variable
'cross_compiling' is set to 'yes', use an alternate method to get the
results instead of calling the macros.


File: autoconf.info,  Node: Guidelines,  Next: Test Functions,  Prev: Test Programs,  Up: Run Time

6.4.2 Guidelines for Test Programs
----------------------------------

Test programs should not write anything to the standard output.  They
should return 0 if the test succeeds, nonzero otherwise, so that success
can be distinguished easily from a core dump or other failure;
segmentation violations and other failures produce a nonzero exit
status.  Test programs should 'exit', not 'return', from 'main', because
on some systems (old Suns, at least) the argument to 'return' in 'main'
is ignored.

   Test programs can use '#if' or '#ifdef' to check the values of
preprocessor macros defined by tests that have already run.  For
example, if you call 'AC_HEADER_STDC', then later on in 'configure.ac'
you can have a test program that includes an ANSI C header file
conditionally:

     #if STDC_HEADERS
     # include <stdlib.h>
     #endif

   If a test program needs to use or create a data file, give it a name
that starts with 'conftest', such as 'conftest.data'.  The 'configure'
script cleans up by running 'rm -rf conftest*' after running test
programs and if the script is interrupted.


File: autoconf.info,  Node: Test Functions,  Prev: Guidelines,  Up: Run Time

6.4.3 Test Functions
--------------------

Function declarations in test programs should have a prototype
conditionalized for C++.  In practice, though, test programs rarely need
functions that take arguments.

     #ifdef __cplusplus
     foo (int i)
     #else
     foo (i) int i;
     #endif

   Functions that test programs declare should also be conditionalized
for C++, which requires 'extern "C"' prototypes.  Make sure to not
include any header files containing clashing prototypes.

     #ifdef __cplusplus
     extern "C" void *malloc (size_t);
     #else
     char *malloc ();
     #endif

   If a test program calls a function with invalid parameters (just to
see whether it exists), organize the program to ensure that it never
invokes that function.  You can do this by calling it in another
function that is never invoked.  You can't do it by putting it after a
call to 'exit', because GCC version 2 knows that 'exit' never returns
and optimizes out any code that follows it in the same block.

   If you include any header files, make sure to call the functions
relevant to them with the correct number of arguments, even if they are
just 0, to avoid compilation errors due to prototypes.  GCC version 2
has internal prototypes for several functions that it automatically
inlines; for example, 'memcpy'.  To avoid errors when checking for them,
either pass them the correct number of arguments or redeclare them with
a different return type (such as 'char').


File: autoconf.info,  Node: Systemology,  Next: Multiple Cases,  Prev: Run Time,  Up: Writing Tests

6.5 Systemology
===============

This section aims at presenting some systems and pointers to
documentation.  It may help you addressing particular problems reported
by users.

QNX 4.25
     QNX is a realtime operating system running on Intel architecture
     meant to be scalable from the small embedded systems to hundred
     processor super-computer.  It claims to be POSIX certified.  More
     information is available on the QNX home page(1), including the QNX
     man pages(2).

   ---------- Footnotes ----------

   (1) QNX home page, <www.qnx.com>.

   (2) QNX man pages, <http://support.qnx.com/support/docs/qnx4/>.


File: autoconf.info,  Node: Multiple Cases,  Next: Language Choice,  Prev: Systemology,  Up: Writing Tests

6.6 Multiple Cases
==================

Some operations are accomplished in several possible ways, depending on
the UNIX variant.  Checking for them essentially requires a "case
statement".  Autoconf does not directly provide one; however, it is easy
to simulate by using a shell variable to keep track of whether a way to
perform the operation has been found yet.

   Here is an example that uses the shell variable 'fstype' to keep
track of whether the remaining cases need to be checked.

     AC_MSG_CHECKING([how to get file system type])
     fstype=no
     # The order of these tests is important.
     AC_TRY_CPP([#include <sys/statvfs.h>
     #include <sys/fstyp.h>],
                [AC_DEFINE(FSTYPE_STATVFS) fstype=SVR4])
     if test $fstype = no; then
       AC_TRY_CPP([#include <sys/statfs.h>
     #include <sys/fstyp.h>],
                  [AC_DEFINE(FSTYPE_USG_STATFS) fstype=SVR3])
     fi
     if test $fstype = no; then
       AC_TRY_CPP([#include <sys/statfs.h>
     #include <sys/vmount.h>],
                  [AC_DEFINE(FSTYPE_AIX_STATFS) fstype=AIX])
     fi
     # (more cases omitted here)
     AC_MSG_RESULT([$fstype])


File: autoconf.info,  Node: Language Choice,  Prev: Multiple Cases,  Up: Writing Tests

6.7 Language Choice
===================

Autoconf-generated 'configure' scripts check for the C compiler and its
features by default.  Packages that use other programming languages
(maybe more than one, e.g.  C and C++) need to test features of the
compilers for the respective languages.  The following macros determine
which programming language is used in the subsequent tests in
'configure.ac'.

 -- Macro: AC_LANG (LANGUAGE)
     Do compilation tests using the compiler, preprocessor and file
     extensions for the specified LANGUAGE.

     Supported languages are:

     'C'
          Do compilation tests using 'CC' and 'CPP' and use extension
          '.c' for test programs.

     'C++'
          Do compilation tests using 'CXX' and 'CXXCPP' and use
          extension '.C' for test programs.

     'Fortran 77'
          Do compilation tests using 'F77' and use extension '.f' for
          test programs.

 -- Macro: AC_LANG_PUSH (LANGUAGE)
     Remember the current language (as set by 'AC_LANG') on a stack, and
     then select the LANGUAGE.  Use this macro and 'AC_LANG_POP' in
     macros that need to temporarily switch to a particular language.

 -- Macro: AC_LANG_POP ([LANGUAGE])
     Select the language that is saved on the top of the stack, as set
     by 'AC_LANG_PUSH', and remove it from the stack.

     If given, LANGUAGE specifies the language we just _quit_.  It is a
     good idea to specify it when it's known (which should be the
     case...), since Autoconf will detect inconsistencies.

          AC_LANG_PUSH(Fortran 77)
          # Perform some tests on Fortran 77.
          # ...
          AC_LANG_POP(Fortran 77)

 -- Macro: AC_REQUIRE_CPP
     Ensure that whichever preprocessor would currently be used for
     tests has been found.  Calls 'AC_REQUIRE' (*note Prerequisite
     Macros::) with an argument of either 'AC_PROG_CPP' or
     'AC_PROG_CXXCPP', depending on which language is current.


File: autoconf.info,  Node: Results,  Next: Programming in M4,  Prev: Writing Tests,  Up: Top

7 Results of Tests
******************

Once 'configure' has determined whether a feature exists, what can it do
to record that information?  There are four sorts of things it can do:
define a C preprocessor symbol, set a variable in the output files, save
the result in a cache file for future 'configure' runs, and print a
message letting the user know the result of the test.

* Menu:

* Defining Symbols::            Defining C preprocessor symbols
* Setting Output Variables::    Replacing variables in output files
* Caching Results::             Speeding up subsequent 'configure' runs
* Printing Messages::           Notifying 'configure' users


File: autoconf.info,  Node: Defining Symbols,  Next: Setting Output Variables,  Prev: Results,  Up: Results

7.1 Defining C Preprocessor Symbols
===================================

A common action to take in response to a feature test is to define a C
preprocessor symbol indicating the results of the test.  That is done by
calling 'AC_DEFINE' or 'AC_DEFINE_UNQUOTED'.

   By default, 'AC_OUTPUT' places the symbols defined by these macros
into the output variable 'DEFS', which contains an option
'-DSYMBOL=VALUE' for each symbol defined.  Unlike in Autoconf version 1,
there is no variable 'DEFS' defined while 'configure' is running.  To
check whether Autoconf macros have already defined a certain C
preprocessor symbol, test the value of the appropriate cache variable,
as in this example:

     AC_CHECK_FUNC(vprintf, [AC_DEFINE(HAVE_VPRINTF)])
     if test "$ac_cv_func_vprintf" != yes; then
       AC_CHECK_FUNC(_doprnt, [AC_DEFINE(HAVE_DOPRNT)])
     fi

   If 'AC_CONFIG_HEADERS' has been called, then instead of creating
'DEFS', 'AC_OUTPUT' creates a header file by substituting the correct
values into '#define' statements in a template file.  *Note
Configuration Headers::, for more information about this kind of output.

 -- Macro: AC_DEFINE (VARIABLE, [VALUE], [DESCRIPTION])
     Define C preprocessor variable VARIABLE.  If VALUE is given, set
     VARIABLE to that value (verbatim), otherwise set it to 1.  VALUE
     should not contain literal newlines, and if you are not using
     'AC_CONFIG_HEADERS' it should not contain any '#' characters, as
     'make' tends to eat them.  To use a shell variable (which you need
     to do in order to define a value containing the M4 quote characters
     '[' or ']'), use 'AC_DEFINE_UNQUOTED' instead.  DESCRIPTION is only
     useful if you are using 'AC_CONFIG_HEADERS'.  In this case,
     DESCRIPTION is put into the generated 'config.h.in' as the comment
     before the macro define.  The following example defines the C
     preprocessor variable 'EQUATION' to be the string constant '"$a >
     $b"':

          AC_DEFINE(EQUATION, "$a > $b")

 -- Macro: AC_DEFINE_UNQUOTED (VARIABLE, [VALUE], [DESCRIPTION])
     Like 'AC_DEFINE', but three shell expansions are
     performed--once--on VARIABLE and VALUE: variable expansion ('$'),
     command substitution ('`'), and backslash escaping ('\').  Single
     and double quote characters in the value have no special meaning.
     Use this macro instead of 'AC_DEFINE' when VARIABLE or VALUE is a
     shell variable.  Examples:

          AC_DEFINE_UNQUOTED(config_machfile, "$machfile")
          AC_DEFINE_UNQUOTED(GETGROUPS_T, $ac_cv_type_getgroups)
          AC_DEFINE_UNQUOTED($ac_tr_hdr)

   Due to the syntactical bizarreness of the Bourne shell, do not use
semicolons to separate 'AC_DEFINE' or 'AC_DEFINE_UNQUOTED' calls from
other macro calls or shell code; that can cause syntax errors in the
resulting 'configure' script.  Use either spaces or newlines.  That is,
do this:

     AC_CHECK_HEADER(elf.h, [AC_DEFINE(SVR4) LIBS="$LIBS -lelf"])

or this:

     AC_CHECK_HEADER(elf.h,
      [AC_DEFINE(SVR4)
       LIBS="$LIBS -lelf"])

instead of this:

     AC_CHECK_HEADER(elf.h, [AC_DEFINE(SVR4); LIBS="$LIBS -lelf"])


File: autoconf.info,  Node: Setting Output Variables,  Next: Caching Results,  Prev: Defining Symbols,  Up: Results

7.2 Setting Output Variables
============================

Another way to record the results of tests is to set "output variables",
which are shell variables whose values are substituted into files that
'configure' outputs.  The two macros below create new output variables.
*Note Preset Output Variables::, for a list of output variables that are
always available.

 -- Macro: AC_SUBST (VARIABLE, [VALUE])
     Create an output variable from a shell variable.  Make 'AC_OUTPUT'
     substitute the variable VARIABLE into output files (typically one
     or more 'Makefile's).  This means that 'AC_OUTPUT' will replace
     instances of '@VARIABLE@' in input files with the value that the
     shell variable VARIABLE has when 'AC_OUTPUT' is called.  This value
     of VARIABLE should not contain literal newlines.

     If VALUE is given, in addition assign it to 'variable'.

 -- Macro: AC_SUBST_FILE (VARIABLE)
     Another way to create an output variable from a shell variable.
     Make 'AC_OUTPUT' insert (without substitutions) the contents of the
     file named by shell variable VARIABLE into output files.  This
     means that 'AC_OUTPUT' will replace instances of '@VARIABLE@' in
     output files (such as 'Makefile.in') with the contents of the file
     that the shell variable VARIABLE names when 'AC_OUTPUT' is called.
     Set the variable to '/dev/null' for cases that do not have a file
     to insert.

     This macro is useful for inserting 'Makefile' fragments containing
     special dependencies or other 'make' directives for particular host
     or target types into 'Makefile's.  For example, 'configure.ac'
     could contain:

          AC_SUBST_FILE(host_frag)
          host_frag=$srcdir/conf/sun4.mh

     and then a 'Makefile.in' could contain:

          @host_frag@

   Running 'configure' in different environments can be extremely
dangerous.  If for instance the user runs 'CC=bizarre-cc ./configure',
then the cache, 'config.h' and many other output files will depend upon
'bizarre-cc' being the C compiler.  If for some reason the user runs
'/configure' again, or if it is run via './config.status --recheck',
(*Note Automatic Remaking::, and *note config.status Invocation::), then
the configuration can be inconsistent, composed of results depending
upon two different compilers.

   Such variables are named "precious variables", and can be declared as
such by 'AC_ARG_VAR'.

 -- Macro: AC_ARG_VAR (VARIABLE, DESCRIPTION)
     Declare VARIABLE is a precious variable, and include its
     DESCRIPTION in the variable section of './configure --help'.

     Being precious means that
        - VARIABLE is 'AC_SUBST''d.

        - VARIABLE is kept in the cache including if it was not
          specified on the './configure' command line.  Indeed, while
          'configure' can notice the definition of 'CC' in './configure
          CC=bizarre-cc', it is impossible to notice it in
          'CC=bizarre-cc ./configure', which, unfortunately, is what
          most users do.

        - VARIABLE is checked for consistency between two 'configure'
          runs.  For instance:

               $ ./configure --silent --config-cache
               $ CC=cc ./configure --silent --config-cache
               configure: error: `CC' was not set in the previous run
               configure: error: changes in the environment can compromise \
               the build
               configure: error: run `make distclean' and/or \
               `rm config.cache' and start over

          and similarly if the variable is unset, or if its content is
          changed.

        - VARIABLE is kept during automatic reconfiguration (*note
          config.status Invocation::) as if it had been passed as a
          command line argument, including when no cache is used:

               $ CC=/usr/bin/cc ./configure undeclared_var=raboof --silent
               $ ./config.status --recheck
               running /bin/sh ./configure undeclared_var=raboof --silent \
                 CC=/usr/bin/cc  --no-create --no-recursion


File: autoconf.info,  Node: Caching Results,  Next: Printing Messages,  Prev: Setting Output Variables,  Up: Results

7.3 Caching Results
===================

To avoid checking for the same features repeatedly in various
'configure' scripts (or in repeated runs of one script), 'configure' can
optionally save the results of many checks in a "cache file" (*note
Cache Files::).  If a 'configure' script runs with caching enabled and
finds a cache file, it reads the results of previous runs from the cache
and avoids rerunning those checks.  As a result, 'configure' can then
run much faster than if it had to perform all of the checks every time.

 -- Macro: AC_CACHE_VAL (CACHE-ID, COMMANDS-TO-SET-IT)
     Ensure that the results of the check identified by CACHE-ID are
     available.  If the results of the check were in the cache file that
     was read, and 'configure' was not given the '--quiet' or '--silent'
     option, print a message saying that the result was cached;
     otherwise, run the shell commands COMMANDS-TO-SET-IT.  If the shell
     commands are run to determine the value, the value will be saved in
     the cache file just before 'configure' creates its output files.
     *Note Cache Variable Names::, for how to choose the name of the
     CACHE-ID variable.

     The COMMANDS-TO-SET-IT _must have no side effects_ except for
     setting the variable CACHE-ID, see below.

 -- Macro: AC_CACHE_CHECK (MESSAGE, CACHE-ID, COMMANDS-TO-SET-IT)
     A wrapper for 'AC_CACHE_VAL' that takes care of printing the
     messages.  This macro provides a convenient shorthand for the most
     common way to use these macros.  It calls 'AC_MSG_CHECKING' for
     MESSAGE, then 'AC_CACHE_VAL' with the CACHE-ID and COMMANDS
     arguments, and 'AC_MSG_RESULT' with CACHE-ID.

     The COMMANDS-TO-SET-IT _must have no side effects_ except for
     setting the variable CACHE-ID, see below.

   It is very common to find buggy macros using 'AC_CACHE_VAL' or
'AC_CACHE_CHECK', because people are tempted to call 'AC_DEFINE' in the
COMMANDS-TO-SET-IT.  Instead, the code that _follows_ the call to
'AC_CACHE_VAL' should call 'AC_DEFINE', by examining the value of the
cache variable.  For instance, the following macro is broken:

     AC_DEFUN([AC_SHELL_TRUE],
     [AC_CACHE_CHECK([whether true(1) works], [ac_cv_shell_true_works],
                     [ac_cv_shell_true_works=no
                      true && ac_cv_shell_true_works=yes
                      if test $ac_cv_shell_true_works = yes; then
                        AC_DEFINE([TRUE_WORKS], 1
                                  [Define if `true(1)' works properly.])
                      fi])
     ])

This fails if the cache is enabled: the second time this macro is run,
'TRUE_WORKS' _will not be defined_.  The proper implementation is:

     AC_DEFUN([AC_SHELL_TRUE],
     [AC_CACHE_CHECK([whether true(1) works], [ac_cv_shell_true_works],
                     [ac_cv_shell_true_works=no
                      true && ac_cv_shell_true_works=yes])
      if test $ac_cv_shell_true_works = yes; then
        AC_DEFINE([TRUE_WORKS], 1
                  [Define if `true(1)' works properly.])
      fi
     ])

   Also, COMMANDS-TO-SET-IT should not print any messages, for example
with 'AC_MSG_CHECKING'; do that before calling 'AC_CACHE_VAL', so the
messages are printed regardless of whether the results of the check are
retrieved from the cache or determined by running the shell commands.

* Menu:

* Cache Variable Names::        Shell variables used in caches
* Cache Files::                 Files 'configure' uses for caching
* Cache Checkpointing::         Loading and saving the cache file


File: autoconf.info,  Node: Cache Variable Names,  Next: Cache Files,  Prev: Caching Results,  Up: Caching Results

7.3.1 Cache Variable Names
--------------------------

The names of cache variables should have the following format:

     PACKAGE-PREFIX_cv_VALUE-TYPE_SPECIFIC-VALUE_[ADDITIONAL-OPTIONS]

for example, 'ac_cv_header_stat_broken' or 'ac_cv_prog_gcc_traditional'.
The parts of the variable name are:

PACKAGE-PREFIX
     An abbreviation for your package or organization; the same prefix
     you begin local Autoconf macros with, except lowercase by
     convention.  For cache values used by the distributed Autoconf
     macros, this value is 'ac'.

'_cv_'
     Indicates that this shell variable is a cache value.  This string
     _must_ be present in the variable name, including the leading
     underscore.

VALUE-TYPE
     A convention for classifying cache values, to produce a rational
     naming system.  The values used in Autoconf are listed in *note
     Macro Names::.

SPECIFIC-VALUE
     Which member of the class of cache values this test applies to.
     For example, which function ('alloca'), program ('gcc'), or output
     variable ('INSTALL').

ADDITIONAL-OPTIONS
     Any particular behavior of the specific member that this test
     applies to.  For example, 'broken' or 'set'.  This part of the name
     may be omitted if it does not apply.

   The values assigned to cache variables may not contain newlines.
Usually, their values will be boolean ('yes' or 'no') or the names of
files or functions; so this is not an important restriction.


File: autoconf.info,  Node: Cache Files,  Next: Cache Checkpointing,  Prev: Cache Variable Names,  Up: Caching Results

7.3.2 Cache Files
-----------------

A cache file is a shell script that caches the results of configure
tests run on one system so they can be shared between configure scripts
and configure runs.  It is not useful on other systems.  If its contents
are invalid for some reason, the user may delete or edit it.

   By default, 'configure' uses no cache file (technically, it uses
'--cache-file=/dev/null'), to avoid problems caused by accidental use of
stale cache files.

   To enable caching, 'configure' accepts '--config-cache' (or '-C') to
cache results in the file 'config.cache'.  Alternatively,
'--cache-file=FILE' specifies that FILE be the cache file.  The cache
file is created if it does not exist already.  When 'configure' calls
'configure' scripts in subdirectories, it uses the '--cache-file'
argument so that they share the same cache.  *Note Subdirectories::, for
information on configuring subdirectories with the 'AC_CONFIG_SUBDIRS'
macro.

   'config.status' only pays attention to the cache file if it is given
the '--recheck' option, which makes it rerun 'configure'.

   It is wrong to try to distribute cache files for particular system
types.  There is too much room for error in doing that, and too much
administrative overhead in maintaining them.  For any features that
can't be guessed automatically, use the standard method of the canonical
system type and linking files (*note Manual Configuration::).

   The site initialization script can specify a site-wide cache file to
use, instead of the usual per-program cache.  In this case, the cache
file will gradually accumulate information whenever someone runs a new
'configure' script.  (Running 'configure' merges the new cache results
with the existing cache file.)  This may cause problems, however, if the
system configuration (e.g.  the installed libraries or compilers)
changes and the stale cache file is not deleted.


File: autoconf.info,  Node: Cache Checkpointing,  Prev: Cache Files,  Up: Caching Results

7.3.3 Cache Checkpointing
-------------------------

If your configure script, or a macro called from configure.ac, happens
to abort the configure process, it may be useful to checkpoint the cache
a few times at key points using 'AC_CACHE_SAVE'.  Doing so will reduce
the amount of time it takes to re-run the configure script with
(hopefully) the error that caused the previous abort corrected.

 -- Macro: AC_CACHE_LOAD
     Loads values from existing cache file, or creates a new cache file
     if a cache file is not found.  Called automatically from 'AC_INIT'.

 -- Macro: AC_CACHE_SAVE
     Flushes all cached values to the cache file.  Called automatically
     from 'AC_OUTPUT', but it can be quite useful to call
     'AC_CACHE_SAVE' at key points in configure.ac.

   For instance:

      ... AC_INIT, etc. ...
     # Checks for programs.
     AC_PROG_CC
     AC_PROG_GCC_TRADITIONAL
      ... more program checks ...
     AC_CACHE_SAVE

     # Checks for libraries.
     AC_CHECK_LIB(nsl, gethostbyname)
     AC_CHECK_LIB(socket, connect)
      ... more lib checks ...
     AC_CACHE_SAVE

     # Might abort...
     AM_PATH_GTK(1.0.2,, (exit 1); exit)
     AM_PATH_GTKMM(0.9.5,, (exit 1); exit)
      ... AC_OUTPUT, etc. ...


File: autoconf.info,  Node: Printing Messages,  Prev: Caching Results,  Up: Results

7.4 Printing Messages
=====================

'configure' scripts need to give users running them several kinds of
information.  The following macros print messages in ways appropriate
for each kind.  The arguments to all of them get enclosed in shell
double quotes, so the shell performs variable and back-quote
substitution on them.

   These macros are all wrappers around the 'echo' shell command.
'configure' scripts should rarely need to run 'echo' directly to print
messages for the user.  Using these macros makes it easy to change how
and when each kind of message is printed; such changes need only be made
to the macro definitions and all of the callers will change
automatically.

   To diagnose static issues, i.e., when 'autoconf' is run, see *note
Reporting Messages::.

 -- Macro: AC_MSG_CHECKING (FEATURE-DESCRIPTION)
     Notify the user that 'configure' is checking for a particular
     feature.  This macro prints a message that starts with 'checking '
     and ends with '...' and no newline.  It must be followed by a call
     to 'AC_MSG_RESULT' to print the result of the check and the
     newline.  The FEATURE-DESCRIPTION should be something like 'whether
     the Fortran compiler accepts C++ comments' or 'for c89'.

     This macro prints nothing if 'configure' is run with the '--quiet'
     or '--silent' option.

 -- Macro: AC_MSG_RESULT (RESULT-DESCRIPTION)
     Notify the user of the results of a check.  RESULT-DESCRIPTION is
     almost always the value of the cache variable for the check,
     typically 'yes', 'no', or a file name.  This macro should follow a
     call to 'AC_MSG_CHECKING', and the RESULT-DESCRIPTION should be the
     completion of the message printed by the call to 'AC_MSG_CHECKING'.

     This macro prints nothing if 'configure' is run with the '--quiet'
     or '--silent' option.

 -- Macro: AC_MSG_NOTICE (MESSAGE)
     Deliver the MESSAGE to the user.  It is useful mainly to print a
     general description of the overall purpose of a group of feature
     checks, e.g.,

          AC_MSG_NOTICE([checking if stack overflow is detectable])

     This macro prints nothing if 'configure' is run with the '--quiet'
     or '--silent' option.

 -- Macro: AC_MSG_ERROR (ERROR-DESCRIPTION, [EXIT-STATUS])
     Notify the user of an error that prevents 'configure' from
     completing.  This macro prints an error message to the standard
     error output and exits 'configure' with EXIT-STATUS (1 by default).
     ERROR-DESCRIPTION should be something like 'invalid value $HOME for
     \$HOME'.

     The ERROR-DESCRIPTION should start with a lower-case letter, and
     "cannot" is preferred to "can't".

 -- Macro: AC_MSG_WARN (PROBLEM-DESCRIPTION)
     Notify the 'configure' user of a possible problem.  This macro
     prints the message to the standard error output; 'configure'
     continues running afterward, so macros that call 'AC_MSG_WARN'
     should provide a default (back-up) behavior for the situations they
     warn about.  PROBLEM-DESCRIPTION should be something like 'ln -s
     seems to make hard links'.


File: autoconf.info,  Node: Programming in M4,  Next: Writing Autoconf Macros,  Prev: Results,  Up: Top

8 Programming in M4
*******************

Autoconf is written on top of two layers: "M4sugar", which provides
convenient macros for pure M4 programming, and "M4sh", which provides
macros dedicated to shell script generation.

   As of this version of Autoconf, these two layers are still
experimental, and their interface might change in the future.  As a
matter of fact, _anything that is not documented must not be used_.

* Menu:

* M4 Quotation::                Protecting macros from unwanted expansion
* Programming in M4sugar::      Convenient pure M4 macros


File: autoconf.info,  Node: M4 Quotation,  Next: Programming in M4sugar,  Prev: Programming in M4,  Up: Programming in M4

8.1 M4 Quotation
================

The most common brokenness of existing macros is an improper quotation.
This section, which users of Autoconf can skip, but which macro writers
_must_ read, first justifies the quotation scheme that was chosen for
Autoconf and then ends with a rule of thumb.  Understanding the former
helps one to follow the latter.

* Menu:

* Active Characters::           Characters that change the behavior of m4
* One Macro Call::              Quotation and one macro call
* Quotation and Nested Macros::  Macros calling macros
* Quadrigraphs::                Another way to escape special characters
* Quotation Rule Of Thumb::     One parenthesis, one quote


File: autoconf.info,  Node: Active Characters,  Next: One Macro Call,  Prev: M4 Quotation,  Up: M4 Quotation

8.1.1 Active Characters
-----------------------

To fully understand where proper quotation is important, you first need
to know what are the special characters in Autoconf: '#' introduces a
comment inside which no macro expansion is performed, ',' separates
arguments, '[' and ']' are the quotes themselves, and finally '(' and
')' (which 'm4' tries to match by pairs).

   In order to understand the delicate case of macro calls, we first
have to present some obvious failures.  Below they are "obvious-ified",
although you find them in real life, they are usually in disguise.

   Comments, introduced by a hash and running up to the newline, are
opaque tokens to the top level: active characters are turned off, and
there is no macro expansion:

     # define([def], ine)
     =># define([def], ine)

   Each time there can be a macro expansion, there is a quotation
expansion; i.e., one level of quotes is stripped:

     int tab[10];
     =>int tab10;
     [int tab[10];]
     =>int tab[10];

   Without this in mind, the reader will try hopelessly to use her macro
'array':

     define([array], [int tab[10];])
     array
     =>int tab10;
     [array]
     =>array

How can you correctly output the intended results(1)?

   ---------- Footnotes ----------

   (1) Using 'defn'.


File: autoconf.info,  Node: One Macro Call,  Next: Quotation and Nested Macros,  Prev: Active Characters,  Up: M4 Quotation

8.1.2 One Macro Call
--------------------

Let's proceed on the interaction between active characters and macros
with this small macro, which just returns its first argument:

     define([car], [$1])

The two pairs of quotes above are not part of the arguments of 'define';
rather, they are understood by the top level when it tries to find the
arguments of 'define'.  Therefore, it is equivalent to write:

     define(car, $1)

But, while it is acceptable for a 'configure.ac' to avoid unneeded
quotes, it is bad practice for Autoconf macros which must both be more
robust and also advocate perfect style.

   At the top level, there are only two possible quotings: either you
quote or you don't:

     car(foo, bar, baz)
     =>foo
     [car(foo, bar, baz)]
     =>car(foo, bar, baz)

   Let's pay attention to the special characters:

     car(#)
     error->EOF in argument list

   The closing parenthesis is hidden in the comment; with a hypothetical
quoting, the top level understood it this way:

     car([#)]

Proper quotation, of course, fixes the problem:

     car([#])
     =>#

   The reader will easily understand the following examples:

     car(foo, bar)
     =>foo
     car([foo, bar])
     =>foo, bar
     car((foo, bar))
     =>(foo, bar)
     car([(foo], [bar)])
     =>(foo
     car([], [])
     =>
     car([[]], [[]])
     =>[]

   With this in mind, we can explore the cases where macros invoke
macros...


File: autoconf.info,  Node: Quotation and Nested Macros,  Next: Quadrigraphs,  Prev: One Macro Call,  Up: M4 Quotation

8.1.3 Quotation and Nested Macros
---------------------------------

The examples below use the following macros:

     define([car], [$1])
     define([active], [ACT, IVE])
     define([array], [int tab[10]])

   Each additional embedded macro call introduces other possible
interesting quotations:

     car(active)
     =>ACT
     car([active])
     =>ACT, IVE
     car([[active]])
     =>active

   In the first case, the top level looks for the arguments of 'car',
and finds 'active'.  Because 'm4' evaluates its arguments before
applying the macro, 'active' is expanded, which results in:

     car(ACT, IVE)
     =>ACT

In the second case, the top level gives 'active' as first and only
argument of 'car', which results in:

     active
     =>ACT, IVE

i.e., the argument is evaluated _after_ the macro that invokes it.  In
the third case, 'car' receives '[active]', which results in:

     [active]
     =>active

exactly as we already saw above.

   The example above, applied to a more realistic example, gives:

     car(int tab[10];)
     =>int tab10;
     car([int tab[10];])
     =>int tab10;
     car([[int tab[10];]])
     =>int tab[10];

Huh?  The first case is easily understood, but why is the second wrong,
and the third right?  To understand that, you must know that after 'm4'
expands a macro, the resulting text is immediately subjected to macro
expansion and quote removal.  This means that the quote removal occurs
twice--first before the argument is passed to the 'car' macro, and
second after the 'car' macro expands to the first argument.

   As the author of the Autoconf macro 'car', you then consider it to be
incorrect that your users have to double-quote the arguments of 'car',
so you "fix" your macro.  Let's call it 'qar' for quoted car:

     define([qar], [[$1]])

and check that 'qar' is properly fixed:

     qar([int tab[10];])
     =>int tab[10];

Ahhh!  That's much better.

   But note what you've done: now that the arguments are literal
strings, if the user wants to use the results of expansions as
arguments, she has to use an _unquoted_ macro call:

     qar(active)
     =>ACT

where she wanted to reproduce what she used to do with 'car':

     car([active])
     =>ACT, IVE

Worse yet: she wants to use a macro that produces a set of 'cpp' macros:

     define([my_includes], [#include <stdio.h>])
     car([my_includes])
     =>#include <stdio.h>
     qar(my_includes)
     error->EOF in argument list

   This macro, 'qar', because it double quotes its arguments, forces its
users to leave their macro calls unquoted, which is dangerous.  Commas
and other active symbols are interpreted by 'm4' before they are given
to the macro, often not in the way the users expect.  Also, because
'qar' behaves differently from the other macros, it's an exception that
should be avoided in Autoconf.


File: autoconf.info,  Node: Quadrigraphs,  Next: Quotation Rule Of Thumb,  Prev: Quotation and Nested Macros,  Up: M4 Quotation

8.1.4 Quadrigraphs
------------------

When writing an autoconf macro you may occasionally need to generate
special characters that are difficult to express with the standard
autoconf quoting rules.  For example, you may need to output the regular
expression '[^[]', which matches any character other than '['.  This
expression contains unbalanced brackets so it cannot be put easily into
an M4 macro.

   You can work around this problem by using one of the following
"quadrigraphs":

'@<:@'
     '['
'@:>@'
     ']'
'@S|@'
     '$'
'@%:@'
     '#'

   Quadrigraphs are replaced at a late stage of the translation process,
after 'm4' is run, so they do not get in the way of M4 quoting.  For
example, the string '[^@<:@]', if properly quoted, will appear as '[^[]'
in the 'configure' script.


File: autoconf.info,  Node: Quotation Rule Of Thumb,  Prev: Quadrigraphs,  Up: M4 Quotation

8.1.5 Quotation Rule Of Thumb
-----------------------------

To conclude, the quotation rule of thumb is:

             _One pair of quotes per pair of parentheses._

   Never over-quote, never under-quote, in particular in the definition
of macros.  In the few places where the macros need to use brackets
(usually in C program text or regular expressions), properly quote _the
arguments_!

   It is common to read Autoconf programs with snippets like:

     AC_TRY_LINK(
     changequote(<<, >>)dnl
     <<#include <time.h>
     #ifndef tzname /* For SGI.  */
     extern char *tzname[]; /* RS6000 and others reject char **tzname.  */
     #endif>>,
     changequote([, ])dnl
     [atoi (*tzname);], ac_cv_var_tzname=yes, ac_cv_var_tzname=no)

which is incredibly useless since 'AC_TRY_LINK' is _already_ double
quoting, so you just need:

     AC_TRY_LINK(
     [#include <time.h>
     #ifndef tzname /* For SGI.  */
     extern char *tzname[]; /* RS6000 and others reject char **tzname.  */
     #endif],
                 [atoi (*tzname);],
                 [ac_cv_var_tzname=yes],
                 [ac_cv_var_tzname=no])

The M4-fluent reader will note that these two examples are rigorously
equivalent, since 'm4' swallows both the 'changequote(<<, >>)' and '<<'
'>>' when it "collects" the arguments: these quotes are not part of the
arguments!

   Simplified, the example above is just doing this:

     changequote(<<, >>)dnl
     <<[]>>
     changequote([, ])dnl

instead of simply:

     [[]]

   With macros that do not double quote their arguments (which is the
rule), double-quote the (risky) literals:

     AC_LINK_IFELSE([AC_LANG_PROGRAM(
     [[#include <time.h>
     #ifndef tzname /* For SGI.  */
     extern char *tzname[]; /* RS6000 and others reject char **tzname.  */
     #endif]],
                                     [atoi (*tzname);])],
                    [ac_cv_var_tzname=yes],
                    [ac_cv_var_tzname=no])

   See *Note Quadrigraphs::, for what to do if you run into a hopeless
case where quoting does not suffice.

   When you create a 'configure' script using newly written macros,
examine it carefully to check whether you need to add more quotes in
your macros.  If one or more words have disappeared in the 'm4' output,
you need more quotes.  When in doubt, quote.

   However, it's also possible to put on too many layers of quotes.  If
this happens, the resulting 'configure' script will contain unexpanded
macros.  The 'autoconf' program checks for this problem by doing 'grep
AC_ configure'.


File: autoconf.info,  Node: Programming in M4sugar,  Prev: M4 Quotation,  Up: Programming in M4

8.2 Programming in M4sugar
==========================

M4 by itself provides only a small, but sufficient, set of all-purpose
macros.  M4sugar introduces additional generic macros.  Its name was
coined by Lars J. Aas: "Readability And Greater Understanding Stands 4
M4sugar".

* Menu:

* Redefined M4 Macros::         M4 builtins changed in M4sugar
* Forbidden Patterns::          Catching unexpanded macros


File: autoconf.info,  Node: Redefined M4 Macros,  Next: Forbidden Patterns,  Prev: Programming in M4sugar,  Up: Programming in M4sugar

8.2.1 Redefined M4 Macros
-------------------------

All the M4 native macros are moved in the 'm4_' pseudo-namespace, e.g.,
M4sugar renames 'define' as 'm4_define' etc.  There is one exception:
'dnl' kept its original name, and no 'm4_dnl' is defined.

   M4sugar redefines some M4 macros, and made them slightly incompatible
with their native equivalent.

 -- Macro: m4_defn (MACRO)
     Contrary to the M4 builtin, this macro fails if MACRO is not
     defined.  See 'm4_undefine'.

 -- Macro: m4_undefine (MACRO)
     Contrary to the M4 builtin, this macro fails if MACRO is not
     defined.  Use

          m4_ifdef([MACRO], [m4_undefine([MACRO])])

     to recover the behavior of the builtin.

 -- Macro: m4_popdef (MACRO)
     Contrary to the M4 builtin, this macro fails if MACRO is not
     defined.  See 'm4_undefine'.


File: autoconf.info,  Node: Forbidden Patterns,  Prev: Redefined M4 Macros,  Up: Programming in M4sugar

8.2.2 Forbidden Patterns
------------------------

M4sugar provides a means to define suspicious patterns, patterns
describing tokens which should not be found in the output.  For
instance, if an Autoconf 'configure' script includes tokens such as
'AC_DEFINE', or 'dnl', then most probably something went wrong
(typically a macro was not evaluated because of over quotation).

   M4sugar forbids all the tokens matching '^m4_' and '^dnl$'.

 -- Macro: m4_pattern_forbid (PATTERN)
     Declare no token matching PATTERN must be found in the output.
     Comments are not checked; this can be a problem if, for instance,
     you have some macro left unexpanded after an '#include'.  No
     consensus is currently found in the Autoconf community, as some
     people consider it should be valid to name macros in comments
     (which doesn't makes sense to the author of this documentation, as
     '#'-comments should document the output, not the input, documented
     vy 'dnl'-comments).

   Of course, you might encounter exceptions to these generic rules, for
instance you might have to refer to '$m4_flags'.

 -- Macro: m4_pattern_allow (PATTERN)
     Any token matching PATTERN is allowed, including if it matches an
     'm4_pattern_forbid' pattern.


File: autoconf.info,  Node: Writing Autoconf Macros,  Next: Portable Shell,  Prev: Programming in M4,  Up: Top

9 Writing Autoconf Macros
*************************

When you write a feature test that could be applicable to more than one
software package, the best thing to do is encapsulate it in a new macro.
Here are some instructions and guidelines for writing Autoconf macros.

* Menu:

* Macro Definitions::           Basic format of an Autoconf macro
* Macro Names::                 What to call your new macros
* Reporting Messages::          Notifying 'autoconf' users
* Dependencies Between Macros::  What to do when macros depend on other macros
* Obsoleting Macros::           Warning about old ways of doing things
* Coding Style::                Writing Autoconf macros à la Autoconf


File: autoconf.info,  Node: Macro Definitions,  Next: Macro Names,  Prev: Writing Autoconf Macros,  Up: Writing Autoconf Macros

9.1 Macro Definitions
=====================

Autoconf macros are defined using the 'AC_DEFUN' macro, which is similar
to the M4 builtin 'define' macro.  In addition to defining a macro,
'AC_DEFUN' adds to it some code that is used to constrain the order in
which macros are called (*note Prerequisite Macros::).

   An Autoconf macro definition looks like this:

     AC_DEFUN(MACRO-NAME, MACRO-BODY)

   You can refer to any arguments passed to the macro as '$1', '$2',
etc.  *Note How to define new macros: (m4.info)Definitions, for more
complete information on writing M4 macros.

   Be sure to properly quote both the MACRO-BODY _and_ the MACRO-NAME to
avoid any problems if the macro happens to have been previously defined.

   Each macro should have a header comment that gives its prototype, and
a brief description.  When arguments have default values, display them
in the prototype.  For example:

     # AC_MSG_ERROR(ERROR, [EXIT-STATUS = 1])
     # --------------------------------------
     define([AC_MSG_ERROR],
     [{ _AC_ECHO([configure: error: $1], 2); exit m4_default([$2], 1); }])

   Comments about the macro should be left in the header comment.  Most
other comments will make their way into 'configure', so just keep using
'#' to introduce comments.

   If you have some very special comments about pure M4 code, comments
that make no sense in 'configure' and in the header comment, then use
the builtin 'dnl': it causes 'm4' to discard the text through the next
newline.

   Keep in mind that 'dnl' is rarely needed to introduce comments; 'dnl'
is more useful to get rid of the newlines following macros that produce
no output, such as 'AC_REQUIRE'.


File: autoconf.info,  Node: Macro Names,  Next: Reporting Messages,  Prev: Macro Definitions,  Up: Writing Autoconf Macros

9.2 Macro Names
===============

All of the Autoconf macros have all-uppercase names starting with 'AC_'
to prevent them from accidentally conflicting with other text.  All
shell variables that they use for internal purposes have
mostly-lowercase names starting with 'ac_'.  To ensure that your macros
don't conflict with present or future Autoconf macros, you should prefix
your own macro names and any shell variables they use with some other
sequence.  Possibilities include your initials, or an abbreviation for
the name of your organization or software package.

   Most of the Autoconf macros' names follow a structured naming
convention that indicates the kind of feature check by the name.  The
macro names consist of several words, separated by underscores, going
from most general to most specific.  The names of their cache variables
use the same convention (*note Cache Variable Names::, for more
information on them).

   The first word of the name after 'AC_' usually tells the category of
feature being tested.  Here are the categories used in Autoconf for
specific test macros, the kind of macro that you are more likely to
write.  They are also used for cache variables, in all-lowercase.  Use
them where applicable; where they're not, invent your own categories.

'C'
     C language builtin features.
'DECL'
     Declarations of C variables in header files.
'FUNC'
     Functions in libraries.
'GROUP'
     UNIX group owners of files.
'HEADER'
     Header files.
'LIB'
     C libraries.
'PATH'
     The full path names to files, including programs.
'PROG'
     The base names of programs.
'MEMBER'
     Members of aggregates.
'SYS'
     Operating system features.
'TYPE'
     C builtin or declared types.
'VAR'
     C variables in libraries.

   After the category comes the name of the particular feature being
tested.  Any further words in the macro name indicate particular aspects
of the feature.  For example, 'AC_FUNC_UTIME_NULL' checks the behavior
of the 'utime' function when called with a 'NULL' pointer.

   An internal macro should have a name that starts with an underscore;
Autoconf internals should therefore start with '_AC_'.  Additionally, a
macro that is an internal subroutine of another macro should have a name
that starts with an underscore and the name of that other macro,
followed by one or more words saying what the internal macro does.  For
example, 'AC_PATH_X' has internal macros '_AC_PATH_X_XMKMF' and
'_AC_PATH_X_DIRECT'.


File: autoconf.info,  Node: Reporting Messages,  Next: Dependencies Between Macros,  Prev: Macro Names,  Up: Writing Autoconf Macros

9.3 Reporting Messages
======================

When macros statically diagnose abnormal situations, benign or fatal,
they should report them using these macros.  For dynamic issues, i.e.,
when 'configure' is run, see *note Printing Messages::.

 -- Macro: AC_DIAGNOSE (CATEGORY, MESSAGE)
     Report MESSAGE as a warning (or as an error if requested by the
     user) if it falls into the CATEGORY.  You are encouraged to use
     standard categories, which currently include:

     'all'
          messages that don't fall into one of the following category.
          Use of an empty CATEGORY is equivalent.

     'cross'
          related to cross compilation issues.

     'obsolete'
          use of an obsolete construct.

     'syntax'
          dubious syntactic constructs, incorrectly ordered macro calls.

 -- Macro: AC_WARNING (MESSAGE)
     Equivalent to 'AC_DIAGNOSE([syntax], MESSAGE)', but you are
     strongly encouraged to use a finer grained category.

 -- Macro: AC_FATAL (MESSAGE)
     Report a severe error MESSAGE, and have 'autoconf' die.

   When the user runs 'autoconf -W error', warnings from 'AC_DIAGNOSE'
and 'AC_WARNING' are reported as error, see *note autoconf Invocation::.


File: autoconf.info,  Node: Dependencies Between Macros,  Next: Obsoleting Macros,  Prev: Reporting Messages,  Up: Writing Autoconf Macros

9.4 Dependencies Between Macros
===============================

Some Autoconf macros depend on other macros having been called first in
order to work correctly.  Autoconf provides a way to ensure that certain
macros are called if needed and a way to warn the user if macros are
called in an order that might cause incorrect operation.

* Menu:

* Prerequisite Macros::         Ensuring required information
* Suggested Ordering::          Warning about possible ordering problems


File: autoconf.info,  Node: Prerequisite Macros,  Next: Suggested Ordering,  Prev: Dependencies Between Macros,  Up: Dependencies Between Macros

9.4.1 Prerequisite Macros
-------------------------

A macro that you write might need to use values that have previously
been computed by other macros.  For example, 'AC_DECL_YYTEXT' examines
the output of 'flex' or 'lex', so it depends on 'AC_PROG_LEX' having
been called first to set the shell variable 'LEX'.

   Rather than forcing the user of the macros to keep track of the
dependencies between them, you can use the 'AC_REQUIRE' macro to do it
automatically.  'AC_REQUIRE' can ensure that a macro is only called if
it is needed, and only called once.

 -- Macro: AC_REQUIRE (MACRO-NAME)
     If the M4 macro MACRO-NAME has not already been called, call it
     (without any arguments).  Make sure to quote MACRO-NAME with square
     brackets.  MACRO-NAME must have been defined using 'AC_DEFUN' or
     else contain a call to 'AC_PROVIDE' to indicate that it has been
     called.

     'AC_REQUIRE' must be used inside an 'AC_DEFUN''d macro; it must not
     be called from the top level.

   'AC_REQUIRE' is often misunderstood.  It really implements
dependencies between macros in the sense that if one macro depends upon
another, the latter will be expanded _before_ the body of the former.
In particular, 'AC_REQUIRE(FOO)' is not replaced with the body of 'FOO'.
For instance, this definition of macros:

     AC_DEFUN([TRAVOLTA],
     [test "$body_temparature_in_celsius" -gt "38" &&
       dance_floor=occupied])
     AC_DEFUN([NEWTON_JOHN],
     [test "$hair_style" = "curly" &&
       dance_floor=occupied])

     AC_DEFUN([RESERVE_DANCE_FLOOR],
     [if date | grep '^Sat.*pm' >/dev/null 2>&1; then
       AC_REQUIRE([TRAVOLTA])
       AC_REQUIRE([NEWTON_JOHN])
     fi])

with this 'configure.ac'

     AC_INIT
     RESERVE_DANCE_FLOOR
     if test "$dance_floor" = occupied; then
       AC_MSG_ERROR([cannot pick up here, let's move])
     fi

will not leave you with a better chance to meet a kindred soul at other
times than Saturday night since it expands into:

     test "$body_temperature_in_Celsius" -gt "38" &&
       dance_floor=occupied
     test "$hair_style" = "curly" &&
       dance_floor=occupied
     fi
     if date | grep '^Sat.*pm' >/dev/null 2>&1; then


     fi

   This behavior was chosen on purpose: (i) it prevents messages in
required macros from interrupting the messages in the requiring macros;
(ii) it avoids bad surprises when shell conditionals are used, as in:

     if ...; then
       AC_REQUIRE([SOME_CHECK])
     fi
     ...
     SOME_CHECK

   You are encouraged to put all 'AC_REQUIRE's at the beginning of a
macro.  You can use 'dnl' to avoid the empty lines they leave.


File: autoconf.info,  Node: Suggested Ordering,  Prev: Prerequisite Macros,  Up: Dependencies Between Macros

9.4.2 Suggested Ordering
------------------------

Some macros should be run before another macro if both are called, but
neither _requires_ that the other be called.  For example, a macro that
changes the behavior of the C compiler should be called before any
macros that run the C compiler.  Many of these dependencies are noted in
the documentation.

   Autoconf provides the 'AC_BEFORE' macro to warn users when macros
with this kind of dependency appear out of order in a 'configure.ac'
file.  The warning occurs when creating 'configure' from 'configure.ac',
not when running 'configure'.

   For example, 'AC_PROG_CPP' checks whether the C compiler can run the
C preprocessor when given the '-E' option.  It should therefore be
called after any macros that change which C compiler is being used, such
as 'AC_PROG_CC'.  So 'AC_PROG_CC' contains:

     AC_BEFORE([$0], [AC_PROG_CPP])dnl

This warns the user if a call to 'AC_PROG_CPP' has already occurred when
'AC_PROG_CC' is called.

 -- Macro: AC_BEFORE (THIS-MACRO-NAME, CALLED-MACRO-NAME)
     Make 'm4' print a warning message to the standard error output if
     CALLED-MACRO-NAME has already been called.  THIS-MACRO-NAME should
     be the name of the macro that is calling 'AC_BEFORE'.  The macro
     CALLED-MACRO-NAME must have been defined using 'AC_DEFUN' or else
     contain a call to 'AC_PROVIDE' to indicate that it has been called.


File: autoconf.info,  Node: Obsoleting Macros,  Next: Coding Style,  Prev: Dependencies Between Macros,  Up: Writing Autoconf Macros

9.5 Obsoleting Macros
=====================

Configuration and portability technology has evolved over the years.
Often better ways of solving a particular problem are developed, or
ad-hoc approaches are systematized.  This process has occurred in many
parts of Autoconf.  One result is that some of the macros are now
considered "obsolete"; they still work, but are no longer considered the
best thing to do, hence they should be replaced with more modern macros.
Ideally, 'autoupdate' should substitute the old macro calls with their
modern implementation.

   Autoconf provides a simple means to obsolete a macro.

 -- Macro: AU_DEFUN (OLD-MACRO, IMPLEMENTATION, [MESSAGE])
     Define OLD-MACRO as IMPLEMENTATION.  The only difference with
     'AC_DEFUN' is that the user will be warned that OLD-MACRO is now
     obsolete.

     If she then uses 'autoupdate', the call to OLD-MACRO will be
     replaced by the modern IMPLEMENTATION.  The additional MESSAGE is
     then printed.


File: autoconf.info,  Node: Coding Style,  Prev: Obsoleting Macros,  Up: Writing Autoconf Macros

9.6 Coding Style
================

The Autoconf macros follow a strict coding style.  You are encouraged to
follow this style, especially if you intend to distribute your macro,
either by contributing it to Autoconf itself, or via other means.

   The first requirement is to pay great attention to the quotation, for
more details, see *note Autoconf Language::, and *note M4 Quotation::.

   Do not try to invent new interfaces.  It is likely that there is a
macro in Autoconf that resembles the macro you are defining: try to
stick to this existing interface (order of arguments, default values,
etc.).  We _are_ conscious that some of these interfaces are not
perfect; nevertheless, when harmless, homogeneity should be preferred
over creativity.

   Be careful about clashes both between M4 symbols and between shell
variables.

   If you stick to the suggested M4 naming scheme (*note Macro Names::),
you are unlikely to generate conflicts.  Nevertheless, when you need to
set a special value, _avoid using a regular macro name_; rather, use an
"impossible" name.  For instance, up to version 2.13, the macro
'AC_SUBST' used to remember what SYMBOLs were already defined by setting
'AC_SUBST_SYMBOL', which is a regular macro name.  But since there is a
macro named 'AC_SUBST_FILE', it was just impossible to 'AC_SUBST(FILE)'!
In this case, 'AC_SUBST(SYMBOL)' or '_AC_SUBST(SYMBOL)' should have been
used (yes, with the parentheses)...or better yet, high-level macros such
as 'AC_EXPAND_ONCE'.

   No Autoconf macro should ever enter the user-variable name space;
i.e., except for the variables that are the actual result of running the
macro, all shell variables should start with 'ac_'.  In addition, small
macros or any macro that is likely to be embedded in other macros should
be careful not to use obvious names.

   Do not use 'dnl' to introduce comments: most of the comments you are
likely to write are either header comments which are not output anyway,
or comments that should make their way into 'configure'.  There are
exceptional cases where you do want to comment special M4 constructs, in
which case 'dnl' is right, but keep in mind that it is unlikely.

   M4 ignores the leading spaces before each argument, use this feature
to indent in such a way that arguments are (more or less) aligned with
the opening parenthesis of the macro being called.  For instance,
instead of

     AC_CACHE_CHECK(for EMX OS/2 environment,
     ac_cv_emxos2,
     [AC_COMPILE_IFELSE([AC_LANG_PROGRAM(, [return __EMX__;])],
     [ac_cv_emxos2=yes], [ac_cv_emxos2=no])])

write

     AC_CACHE_CHECK([for EMX OS/2 environment], [ac_cv_emxos2],
     [AC_COMPILE_IFELSE([AC_LANG_PROGRAM([], [return __EMX__;])],
                        [ac_cv_emxos2=yes],
                        [ac_cv_emxos2=no])])

or even

     AC_CACHE_CHECK([for EMX OS/2 environment],
                    [ac_cv_emxos2],
                    [AC_COMPILE_IFELSE([AC_LANG_PROGRAM([],
                                                        [return __EMX__;])],
                                       [ac_cv_emxos2=yes],
                                       [ac_cv_emxos2=no])])

   When using 'AC_TRY_RUN' or any macro that cannot work when
cross-compiling, provide a pessimistic value (typically 'no').

   Feel free to use various tricks to prevent auxiliary tools, such as
syntax-highlighting editors, from behaving improperly.  For instance,
instead of:

     patsubst([$1], [$"])

use

     patsubst([$1], [$""])

so that Emacsen do not open a endless "string" at the first quote.  For
the same reasons, avoid:

     test $[#] != 0

and use:

     test $[@%:@] != 0

Otherwise, the closing bracket would be hidden inside a '#'-comment,
breaking the bracket-matching highlighting from Emacsen.  Note the
preferred style to escape from M4: '$[1]', '$[@]', etc.  Do not escape
when it is unneeded.  Common examples of useless quotation are '[$]$1'
(write '$$1'), '[$]var' (use '$var'), etc.  If you add portability
issues to the picture, you'll prefer '${1+"$[@]"}' to '"[$]@"', and
you'll prefer do something better than hacking Autoconf ':-)'.

   When using 'sed', don't use '-e' except for indenting purpose.  With
the 's' command, the preferred separator is '/' unless '/' itself is
used in the command, in which case you should use ','.

   *Note Macro Definitions::, for details on how to define a macro.  If
a macro doesn't use 'AC_REQUIRE' and it is expected to never be the
object of an 'AC_REQUIRE' directive, then use 'define'.  In case of
doubt, use 'AC_DEFUN'.  All the 'AC_REQUIRE' statements should be at the
beginning of the macro, 'dnl''ed.

   You should not rely on the number of arguments: instead of checking
whether an argument is missing, test that it is not empty.  It provides
both a simpler and a more predictable interface to the user, and saves
room for further arguments.

   Unless the macro is short, try to leave the closing '])' at the
beginning of a line, followed by a comment that repeats the name of the
macro being defined.  This introduces an additional newline in
'configure'; normally, that is not a problem, but if you want to remove
it you can use '[]dnl' on the last line.  You can similarly use '[]dnl'
after a macro call to remove its newline.  '[]dnl' is recommended
instead of 'dnl' to ensure that M4 does not interpret the 'dnl' as being
attached to the preceding text or macro output.  For example, instead
of:

     AC_DEFUN([AC_PATH_X],
     [AC_MSG_CHECKING([for X])
     AC_REQUIRE_CPP()
     # ...omitted...
       AC_MSG_RESULT([libraries $x_libraries, headers $x_includes])
     fi])

you would write:

     AC_DEFUN([AC_PATH_X],
     [AC_REQUIRE_CPP()[]dnl
     AC_MSG_CHECKING([for X])
     # ...omitted...
       AC_MSG_RESULT([libraries $x_libraries, headers $x_includes])
     fi[]dnl
     ])# AC_PATH_X

   If the macro is long, try to split it into logical chunks.
Typically, macros that check for a bug in a function and prepare its
'AC_LIBOBJ' replacement should have an auxiliary macro to perform this
setup.  Do not hesitate to introduce auxiliary macros to factor your
code.

   In order to highlight the recommended coding style, here is a macro
written the old way:

     dnl Check for EMX on OS/2.
     dnl _AC_EMXOS2
     AC_DEFUN(_AC_EMXOS2,
     [AC_CACHE_CHECK(for EMX OS/2 environment, ac_cv_emxos2,
     [AC_COMPILE_IFELSE([AC_LANG_PROGRAM(, return __EMX__;)],
     ac_cv_emxos2=yes, ac_cv_emxos2=no)])
     test "$ac_cv_emxos2" = yes && EMXOS2=yes])

and the new way:

     # _AC_EMXOS2
     # ----------
     # Check for EMX on OS/2.
     define([_AC_EMXOS2],
     [AC_CACHE_CHECK([for EMX OS/2 environment], [ac_cv_emxos2],
     [AC_COMPILE_IFELSE([AC_LANG_PROGRAM([], [return __EMX__;])],
                        [ac_cv_emxos2=yes],
                        [ac_cv_emxos2=no])])
     test "$ac_cv_emxos2" = yes && EMXOS2=yes[]dnl
     ])# _AC_EMXOS2


File: autoconf.info,  Node: Portable Shell,  Next: Manual Configuration,  Prev: Writing Autoconf Macros,  Up: Top

10 Portable Shell Programming
*****************************

When writing your own checks, there are some shell-script programming
techniques you should avoid in order to make your code portable.  The
Bourne shell and upward-compatible shells like the Korn shell and Bash
have evolved over the years, but to prevent trouble, do not take
advantage of features that were added after UNIX version 7, circa 1977.
You should not use shell functions, aliases, negated character classes,
or other features that are not found in all Bourne-compatible shells;
restrict yourself to the lowest common denominator.  Even 'unset' is not
supported by all shells!  Also, include a space after the exclamation
point in interpreter specifications, like this:

     #! /usr/bin/perl

If you omit the space before the path, then 4.2BSD based systems (such
as Sequent DYNIX) will ignore the line, because they interpret '#! /' as
a 4-byte magic number.

   The set of external programs you should run in a 'configure' script
is fairly small.  *Note Utilities in Makefiles: (standards)Utilities in
Makefiles, for the list.  This restriction allows users to start out
with a fairly small set of programs and build the rest, avoiding too
many interdependencies between packages.

   Some of these external utilities have a portable subset of features;
see *note Limitations of Usual Tools::.

* Menu:

* Shellology::                  A zoology of shells
* Here-Documents::              Quirks and tricks
* File Descriptors::            FDs and redirections
* File System Conventions::     File- and pathnames
* Shell Substitutions::         Variable and command expansions
* Assignments::                 Varying side effects of assignments
* Special Shell Variables::     Variables you should not change
* Limitations of Builtins::     Portable use of not so portable /bin/sh
* Limitations of Usual Tools::  Portable use of portable tools
* Limitations of Make::         Portable Makefiles


File: autoconf.info,  Node: Shellology,  Next: Here-Documents,  Prev: Portable Shell,  Up: Portable Shell

10.1 Shellology
===============

There are several families of shells, most prominently the Bourne family
and the C shell family which are deeply incompatible.  If you want to
write portable shell scripts, avoid members of the C shell family.

   Below we describe some of the members of the Bourne shell family.

Ash
     'ash' is often used on GNU/Linux and BSD systems as a light-weight
     Bourne-compatible shell.  Ash 0.2 has some bugs that are fixed in
     the 0.3.x series, but portable shell scripts should workaround
     them, since version 0.2 is still shipped with many GNU/Linux
     distributions.

     To be compatible with Ash 0.2:

        - don't use '$?' after expanding empty or unset variables:

               foo=
               false
               $foo
               echo "Don't use it: $?"

        - don't use command substitution within variable expansion:

               cat ${FOO=`bar`}

        - beware that single builtin substitutions are not performed by
          a sub shell, hence their effect applies to the current shell!
          *Note Shell Substitutions::, item "Command Substitution".

Bash
     To detect whether you are running 'bash', test if 'BASH_VERSION' is
     set.  To disable its extensions and require POSIX compatibility,
     run 'set -o posix'.  *Note Bash POSIX Mode: (bash)Bash POSIX Mode,
     for details.

'/usr/xpg4/bin/sh' on Solaris
     The POSIX-compliant Bourne shell on a Solaris system is
     '/usr/xpg4/bin/sh' and is part of an extra optional package.  There
     is no extra charge for this package, but it is also not part of a
     minimal OS install and therefore some folks may not have it.

Zsh
     To detect whether you are running 'zsh', test if 'ZSH_VERSION' is
     set.  By default 'zsh' is _not_ compatible with the Bourne shell:
     you have to run 'emulate sh' and set 'NULLCMD' to ':'.  *Note
     Compatibility: (zsh)Compatibility, for details.

     Zsh 3.0.8 is the native '/bin/sh' on Mac OS X 10.0.3.

   The following discussion between Russ Allbery and Robert Lipe is
worth reading:

Russ Allbery:

     The GNU assumption that '/bin/sh' is the one and only shell leads
     to a permanent deadlock.  Vendors don't want to break user's
     existent shell scripts, and there are some corner cases in the
     Bourne shell that are not completely compatible with a POSIX shell.
     Thus, vendors who have taken this route will _never_ (OK..."never
     say never") replace the Bourne shell (as '/bin/sh') with a POSIX
     shell.

Robert Lipe:

     This is exactly the problem.  While most (at least most System V's)
     do have a bourne shell that accepts shell functions most vendor
     '/bin/sh' programs are not the POSIX shell.

     So while most modern systems do have a shell _somewhere_ that meets
     the POSIX standard, the challenge is to find it.


File: autoconf.info,  Node: Here-Documents,  Next: File Descriptors,  Prev: Shellology,  Up: Portable Shell

10.2 Here-Documents
===================

Don't rely on '\' being preserved just because it has no special meaning
together with the next symbol.  in the native '/bin/sh' on OpenBSD 2.7
'\"' expands to '"' in here-documents with unquoted delimiter.  As a
general rule, if '\\' expands to '\' use '\\' to get '\'.

   With OpenBSD 2.7's '/bin/sh'

     $ cat <<EOF
     > \" \\
     > EOF
     " \

and with Bash:

     bash-2.04$ cat <<EOF
     > \" \\
     > EOF
     \" \

   Many older shells (including the Bourne shell) implement
here-documents inefficiently.  Users can generally speed things up by
using a faster shell, e.g., by using the command 'bash ./configure'
rather than plain './configure'.

   Some shells can be extremely inefficient when there are a lot of
here-documents inside a single statement.  For instance if your
'configure.ac' includes something like:

     if <cross_compiling>; then
       assume this and that
     else
       check this
       check that
       check something else
       ...
       on and on forever
       ...
     fi

   A shell parses the whole 'if'/'fi' construct, creating temporary
files for each here document in it.  Some shells create links for such
here-documents on every 'fork', so that the clean-up code they had
installed correctly removes them.  It is creating the links that the
shell can take forever.

   Moving the tests out of the 'if'/'fi', or creating multiple 'if'/'fi'
constructs, would improve the performance significantly.  Anyway, this
kind of construct is not exactly the typical use of Autoconf.  In fact,
it's even not recommended, because M4 macros can't look into shell
conditionals, so we may fail to expand a macro when it was expanded
before in a conditional path, and the condition turned out to be false
at run-time, and we end up not executing the macro at all.


File: autoconf.info,  Node: File Descriptors,  Next: File System Conventions,  Prev: Here-Documents,  Up: Portable Shell

10.3 File Descriptors
=====================

Some file descriptors shall not be used, since some systems, admittedly
arcane, use them for special purpose:

3
     some systems may open it to '/dev/tty'.

4
     used on the Kubota Titan.

   Don't redirect several times the same file descriptor, as you are
doomed to failure under Ultrix.

     ULTRIX V4.4 (Rev. 69) System #31: Thu Aug 10 19:42:23 GMT 1995
     UWS V4.4 (Rev. 11)
     $ eval 'echo matter >fullness' >void
     illegal io
     $ eval '(echo matter >fullness)' >void
     illegal io
     $ (eval '(echo matter >fullness)') >void
     Ambiguous output redirect.

In each case the expected result is of course 'fullness' containing
'matter' and 'void' being empty.

   Don't try to redirect the standard error of a command substitution:
it must be done _inside_ the command substitution: when running ': `cd
/zorglub` 2>/dev/null' expect the error message to escape, while ': `cd
/zorglub 2>/dev/null`' works properly.

   It is worth noting that Zsh (but not Ash nor Bash) makes it possible
in assignments though: 'foo=`cd /zorglub` 2>/dev/null'.

   Most shells, if not all (including Bash, Zsh, Ash), output traces on
stderr, even for sub-shells.  This might result in undesired content if
you meant to capture the standard-error output of the inner command:

     $ ash -x -c '(eval "echo foo >&2") 2>stderr'
     $ cat stderr
     + eval echo foo >&2
     + echo foo
     foo
     $ bash -x -c '(eval "echo foo >&2") 2>stderr'
     $ cat stderr
     + eval 'echo foo >&2'
     ++ echo foo
     foo
     $ zsh -x -c '(eval "echo foo >&2") 2>stderr'
     # Traces on startup files deleted here.
     $ cat stderr
     +zsh:1> eval echo foo >&2
     +zsh:1> echo foo
     foo

You'll appreciate the various levels of detail...

   One workaround is to grep out uninteresting lines, hoping not to
remove good ones...


File: autoconf.info,  Node: File System Conventions,  Next: Shell Substitutions,  Prev: File Descriptors,  Up: Portable Shell

10.4 File System Conventions
============================

While 'autoconf' and friends will usually be run on some Unix variety,
it can and will be used on other systems, most notably DOS variants.
This impacts several assumptions regarding file and path names.

For example, the following code:

     case $foo_dir in
       /*) # Absolute
          ;;
       *)
          foo_dir=$dots$foo_dir ;;
     esac

will fail to properly detect absolute paths on those systems, because
they can use a drivespec, and will usually use a backslash as directory
separator.  The canonical way to check for absolute paths is:

     case $foo_dir in
       [\\/]* | ?:[\\/]* ) # Absolute
          ;;
       *)
          foo_dir=$dots$foo_dir ;;
     esac

Make sure you quote the brackets if appropriate and keep the backslash
as first character (*note Limitations of Builtins::).

   Also, because the colon is used as part of a drivespec, these systems
don't use it as path separator.  When creating or accessing paths, use
'$ac_path_separator' instead (or the 'PATH_SEPARATOR' output variable).
'autoconf' sets this to the appropriate value (':' or ';') when it
starts up.

   File names need extra care as well.  While DOS-based environments
that are Unixy enough to run 'autoconf' (such as DJGPP) will usually be
able to handle long file names properly, there are still limitations
that can seriously break packages.  Several of these issues can be
easily detected by the doschk(1) package.

   A short overview follows; problems are marked with SFN/LFN to
indicate where they apply: SFN means the issues are only relevant to
plain DOS, not to DOS boxes under Windows, while LFN identifies problems
that exist even under Windows.

No multiple dots (SFN)
     DOS cannot handle multiple dots in filenames.  This is an
     especially important thing to remember when building a portable
     configure script, as 'autoconf' uses a .in suffix for template
     files.

     This is perfectly OK on Unices:

          AC_CONFIG_HEADER(config.h)
          AC_CONFIG_FILES([source.c foo.bar])
          AC_OUTPUT

     but it causes problems on DOS, as it requires 'config.h.in',
     'source.c.in' and 'foo.bar.in'.  To make your package more portable
     to DOS-based environments, you should use this instead:

          AC_CONFIG_HEADER(config.h:config.hin)
          AC_CONFIG_FILES([source.c:source.cin foo.bar:foobar.in])
          AC_OUTPUT

No leading dot (SFN)
     DOS cannot handle filenames that start with a dot.  This is usually
     not a very important issue for 'autoconf'.

Case insensitivity (LFN)
     DOS is case insensitive, so you cannot, for example, have both a
     file called 'INSTALL' and a directory called 'install'.  This also
     affects 'make'; if there's a file called 'INSTALL' in the
     directory, 'make install' will do nothing (unless the 'install'
     target is marked as PHONY).

The 8+3 limit (SFN)
     Because the DOS file system only stores the first 8 characters of
     the filename and the first 3 of the extension, those must be
     unique.  That means that 'foobar-part1.c', 'foobar-part2.c' and
     'foobar-prettybird.c' all resolve to the same filename
     ('FOOBAR-P.C').  The same goes for 'foo.bar' and 'foo.bartender'.

     Note: This is not usually a problem under Windows, as it uses
     numeric tails in the short version of filenames to make them
     unique.  However, a registry setting can turn this behaviour off.
     While this makes it possible to share file trees containing long
     file names between SFN and LFN environments, it also means the
     above problem applies there as well.

Invalid characters
     Some characters are invalid in DOS filenames, and should therefore
     be avoided.  In a LFN environment, these are '/', '\', '?', '*',
     ':', '<', '>', '|' and '"'.  In a SFN environment, other characters
     are also invalid.  These include '+', ',', '[' and ']'.

   ---------- Footnotes ----------

   (1) doschk, <ftp://ftp.gnu.org/gnu/non-gnu/doschk/doschk-1.1.tar.gz>.


File: autoconf.info,  Node: Shell Substitutions,  Next: Assignments,  Prev: File System Conventions,  Up: Portable Shell

10.5 Shell Substitutions
========================

Contrary to a persistent urban legend, the Bourne shell does not
systematically split variables and backquoted expressions, in particular
on the right-hand side of assignments and in the argument of 'case'.
For instance, the following code:

     case "$given_srcdir" in
     .)  top_srcdir="`echo "$dots" | sed 's,/$,,'`"
     *)  top_srcdir="$dots$given_srcdir" ;;
     esac

is more readable when written as:

     case $given_srcdir in
     .)  top_srcdir=`echo "$dots" | sed 's,/$,,'`
     *)  top_srcdir=$dots$given_srcdir ;;
     esac

and in fact it is even _more_ portable: in the first case of the first
attempt, the computation of 'top_srcdir' is not portable, since not all
shells properly understand '"`..."..."...`"'.  Worse yet, not all shells
understand '"`...\"...\"...`"' the same way.  There is just no portable
way to use double-quoted strings inside double-quoted backquoted
expressions (pfew!).

'$@'
     One of the most famous shell-portability issues is related to
     '"$@"': when there are no positional arguments, it is supposed to
     be equivalent to nothing.  But some shells, for instance under
     Digital Unix 4.0 and 5.0, will then replace it with an empty
     argument.  To be portable, use '${1+"$@"}'.

'${VAR:-VALUE}'
     Old BSD shells, including the Ultrix 'sh', don't accept the colon
     for any shell substitution, and complain and die.

'${VAR=LITERAL}'
     Be sure to quote:

          : ${var='Some words'}

     otherwise some shells, such as on Digital Unix V 5.0, will die
     because of a "bad substitution".

     Solaris' '/bin/sh' has a frightening bug in its interpretation of
     this.  Imagine you need set a variable to a string containing '}'.
     This '}' character confuses Solaris' '/bin/sh' when the affected
     variable was already set.  This bug can be exercised by running:

          $ unset foo
          $ foo=${foo='}'}
          $ echo $foo
          }
          $ foo=${foo='}'   # no error; this hints to what the bug is
          $ echo $foo
          }
          $ foo=${foo='}'}
          $ echo $foo
          }}
           ^ ugh!

     It seems that '}' is interpreted as matching '${', even though it
     is enclosed in single quotes.  The problem doesn't happen using
     double quotes.

'${VAR=EXPANDED-VALUE}'
     On Ultrix, running

          default="yu,yaa"
          : ${var="$default"}

     will set VAR to 'M-yM-uM-,M-yM-aM-a', i.e., the 8th bit of each
     char will be set.  You won't observe the phenomenon using a simple
     'echo $var' since apparently the shell resets the 8th bit when it
     expands $var.  Here are two means to make this shell confess its
     sins:

          $ cat -v <<EOF
          $var
          EOF

     and

          $ set | grep '^var=' | cat -v

     One classic incarnation of this bug is:

          default="a b c"
          : ${list="$default"}
          for c in $list; do
            echo $c
          done

     You'll get 'a b c' on a single line.  Why?  Because there are no
     spaces in '$list': there are 'M- ', i.e., spaces with the 8th bit
     set, hence no IFS splitting is performed!!!

     One piece of good news is that Ultrix works fine with ':
     ${list=$default}'; i.e., if you _don't_ quote.  The bad news is
     then that QNX 4.25 then sets LIST to the _last_ item of DEFAULT!

     The portable way out consists in using a double assignment, to
     switch the 8th bit twice on Ultrix:

          list=${list="$default"}

     ...but beware of the '}' bug from Solaris (see above).  For safety,
     use:

          test "${var+set}" = set || var={VALUE}

'`COMMANDS`'
     While in general it makes no sense, do not substitute a single
     builtin with side effects as Ash 0.2, trying to optimize, does not
     fork a sub-shell to perform the command.

     For instance, if you wanted to check that 'cd' is silent, do not
     use 'test -z "`cd /`"' because the following can happen:

          $ pwd
          /tmp
          $ test -n "`cd /`" && pwd
          /

     The result of 'foo=`exit 1`' is left as an exercise to the reader.

'$(COMMANDS)'
     This construct is meant to replace '`COMMANDS`'; they can be nested
     while this is impossible to do portably with back quotes.
     Unfortunately it is not yet widely supported.  Most notably, even
     recent releases of Solaris don't support it:

          $ showrev -c /bin/sh | grep version
          Command version: SunOS 5.8 Generic 109324-02 February 2001
          $ echo $(echo blah)
          syntax error: `(' unexpected

     nor does IRIX 6.5's Bourne shell:
          $ uname -a
          IRIX firebird-image 6.5 07151432 IP22
          $ echo $(echo blah)
          $(echo blah)


File: autoconf.info,  Node: Assignments,  Next: Special Shell Variables,  Prev: Shell Substitutions,  Up: Portable Shell

10.6 Assignments
================

When setting several variables in a row, be aware that the order of the
evaluation is undefined.  For instance 'foo=1 foo=2; echo $foo' gives
'1' with sh on Solaris, but '2' with Bash.  You must use ';' to enforce
the order: 'foo=1; foo=2; echo $foo'.

   Don't rely on the exit status of an assignment: Ash 0.2 does not
change the status and propagates that of the last statement:

     $ false || foo=bar; echo $?
     1
     $ false || foo=`:`; echo $?
     0

and to make things even worse, QNX 4.25 just sets the exit status to 0
in any case:

     $ foo=`exit 1`; echo $?
     0

   To assign default values, follow this algorithm:

  1. If the default value is a literal and does not contain any closing
     brace, use:

          : ${var='my literal'}

  2. If the default value contains no closing brace, has to be expanded,
     and the variable being initialized will never be IFS-split (i.e.,
     it's not a list), then use:

          : ${var="$default"}

  3. If the default value contains no closing brace, has to be expanded,
     and the variable being initialized will be IFS-split (i.e., it's a
     list), then use:

          var=${var="$default"}

  4. If the default value contains a closing brace, then use:

          test "${var+set}" = set || var='${indirection}'

   In most cases 'var=${var="$default"}' is fine, but in case of doubt,
just use the latter.  *Note Shell Substitutions::, items '${VAR:-VALUE}'
and '${VAR=VALUE}' for the rationale.


File: autoconf.info,  Node: Special Shell Variables,  Next: Limitations of Builtins,  Prev: Assignments,  Up: Portable Shell

10.7 Special Shell Variables
============================

Some shell variables should not be used, since they can have a deep
influence on the behavior of the shell.  In order to recover a sane
behavior from the shell, some variables should be unset, but 'unset' is
not portable (*note Limitations of Builtins::) and a fallback value is
needed.  We list these values below.

'CDPATH'
     When this variable is set 'cd' is verbose, so idioms such as
     'abs=`cd $rel && pwd`' break because 'abs' receives the path twice.

     Setting 'CDPATH' to the empty value is not enough for most shells.
     A simple colon is enough except for 'zsh', which prefers a leading
     dot:

          zsh-3.1.6 % mkdir foo && (CDPATH=: cd foo)
          /tmp/foo
          zsh-3.1.6 % (CDPATH=:. cd foo)
          /tmp/foo
          zsh-3.1.6 % (CDPATH=.: cd foo)
          zsh-3.1.6 %

     (of course we could just 'unset' 'CDPATH', since it also behaves
     properly if set to the empty string).

     Life wouldn't be so much fun if 'bash' and 'zsh' had the same
     behavior:

          bash-2.02 % (CDPATH=:. cd foo)
          bash-2.02 % (CDPATH=.: cd foo)
          /tmp/foo

     Therefore, a portable solution to neutralize 'CDPATH' is

          CDPATH=${ZSH_VERSION+.}:

     Note that since 'zsh' supports 'unset', you may unset 'CDPATH'
     using ':' as a fallback, see *note Limitations of Builtins::.

'IFS'
     Don't set the first character of 'IFS' to backslash.  Indeed,
     Bourne shells use the first character (backslash) when joining the
     components in '"$@"' and some shells then re-interpret (!)  the
     backslash escapes, so you can end up with backspace and other
     strange characters.

'LANG'
'LC_ALL'
'LC_TIME'
'LC_CTYPE'
'LANGUAGE'
'LC_COLLATE'
'LC_NUMERIC'
'LC_MESSAGES'

     These must not be set unconditionally because not all systems
     understand e.g.  'LANG=C' (notably SCO). Fixing 'LC_MESSAGES'
     prevents Solaris 'sh' from translating var values in 'set'!  Non-C
     'LC_CTYPE' values break the ctype check.  Fixing 'LC_COLLATE' makes
     scripts more portable in some cases.  For example, it causes the
     regular expression '[a-z]' to match only lower-case letters on
     ASCII platforms.  However, '[a-z]' does not work in general even
     when 'LC_COLLATE' is fixed; for example, it does not work for
     EBCDIC platforms.  For maximum portability, you should use regular
     expressions like '[abcdefghijklmnopqrstuvwxyz]' that list
     characters explicitly instead of relying on ranges.

     _If_ one of these variables is set, you should try to unset it,
     using 'C' as a fall back value.  see *note Limitations of
     Builtins::, builtin 'unset', for more details.

'NULLCMD'
     When executing the command '>foo', 'zsh' executes '$NULLCMD >foo'.
     The Bourne shell considers 'NULLCMD' is ':', while 'zsh', even in
     Bourne shell compatibility mode, sets 'NULLCMD' to 'cat'.  If you
     forgot to set 'NULLCMD', your script might be suspended waiting for
     data on its standard input.

'status'
     This variable is an alias to '$?' for 'zsh' (at least 3.1.6), hence
     read-only.  Do not use it.

'PATH_SEPARATOR'
     On DJGPP systems, the 'PATH_SEPARATOR' variable can be set to
     either ':' or ';' to control the path separator 'bash' uses to set
     up certain environment variables (such as 'PATH').  Since this only
     works inside bash, you want autoconf to detect the regular DOS path
     separator ';', so it can be safely substituted in files that may
     not support ';' as path separator.  So either unset this variable
     or set it to ';'.

'RANDOM'
     Many shells provide 'RANDOM', a variable that returns a different
     integer when used.  Most of the time, its value does not change
     when it is not used, but on IRIX 6.5 the value changes all the
     time.  This can be observed by using 'set'.


File: autoconf.info,  Node: Limitations of Builtins,  Next: Limitations of Usual Tools,  Prev: Special Shell Variables,  Up: Portable Shell

10.8 Limitations of Shell Builtins
==================================

No, no, we are serious: some shells do have limitations!  :)

   You should always keep in mind that any built-in or command may
support options, and therefore have a very different behavior with
arguments starting with a dash.  For instance, the innocent 'echo
"$word"' can give unexpected results when 'word' starts with a dash.  It
is often possible to avoid this problem using 'echo "x$word"', taking
the 'x' into account later in the pipe.

'!'
     You can't use '!', you'll have to rewrite your code.

'break'
     The use of 'break 2', etcetera, is safe.

'case'
     You don't need to quote the argument; no splitting is performed.

     You don't need the final ';;', but you should use it.

     Because of a bug in its 'fnmatch', 'bash' fails to properly handle
     backslashes in character classes:

          bash-2.02$ case /tmp in [/\\]*) echo OK;; esac
          bash-2.02$

     This is extremely unfortunate, since you are likely to use this
     code to handle UNIX or MS-DOS absolute paths.  To work around this
     bug, always put the backslash first:

          bash-2.02$ case '\TMP' in [\\/]*) echo OK;; esac
          OK
          bash-2.02$ case /tmp in [\\/]*) echo OK;; esac
          OK

'echo'
     The simple 'echo' is probably the most surprising source of
     portability troubles.  It is not possible to use 'echo' portably
     unless both options and escape sequences are omitted.  New
     applications which are not aiming at portability should use
     'printf' instead of 'echo'.

     Don't expect any option.  *Note Preset Output Variables::, 'ECHO_N'
     etc.  for a means to simulate '-c'.

     Do not use backslashes in the arguments, as there is no consensus
     on their handling.  On 'echo '\n' | wc -l', the 'sh' of Digital
     Unix 4.0, MIPS RISC/OS 4.52, answer 2, but the Solaris' 'sh', Bash
     and Zsh (in 'sh' emulation mode) report 1.  Please note that the
     problem is truly 'echo': all the shells understand ''\n'' as the
     string composed of a backslash and an 'n'.

     Because of these problems, do not pass a string containing
     arbitrary characters to 'echo'.  For example, 'echo "$foo"' is safe
     if you know that FOO's value cannot contain backslashes and cannot
     start with '-', but otherwise you should use a here-document like
     this:

          cat <<EOF
          $foo
          EOF

'exit'
     The default value of 'exit' is supposed to be '$?'; unfortunately,
     some shells, such as the DJGPP port of Bash 2.04, just perform
     'exit 0'.

          bash-2.04$ foo=`exit 1` || echo fail
          fail
          bash-2.04$ foo=`(exit 1)` || echo fail
          fail
          bash-2.04$ foo=`(exit 1); exit` || echo fail
          bash-2.04$

     Using 'exit $?' restores the expected behavior.

     Some shell scripts, such as those generated by 'autoconf', use a
     trap to clean up before exiting.  If the last shell command exited
     with nonzero status, the trap also exits with nonzero status so
     that the invoker can tell that an error occurred.

     Unfortunately, in some shells, such as Solaris 8 'sh', an exit trap
     ignores the 'exit' command's status.  In these shells, a trap
     cannot determine whether it was invoked by plain 'exit' or by 'exit
     1'.  Instead of calling 'exit' directly, use the 'AC_MSG_ERROR'
     macro that has a workaround for this problem.

'export'
     The builtin 'export' dubs "environment variable" a shell variable.
     Each update of exported variables corresponds to an update of the
     environment variables.  Conversely, each environment variable
     received by the shell when it is launched should be imported as a
     shell variable marked as exported.

     Alas, many shells, such as Solaris 2.5, IRIX 6.3, IRIX 5.2, AIX
     4.1.5 and DU 4.0, forget to 'export' the environment variables they
     receive.  As a result, two variables are coexisting: the
     environment variable and the shell variable.  The following code
     demonstrates this failure:

          #! /bin/sh
          echo $FOO
          FOO=bar
          echo $FOO
          exec /bin/sh $0

     when run with 'FOO=foo' in the environment, these shells will print
     alternately 'foo' and 'bar', although it should only print 'foo'
     and then a sequence of 'bar's.

     Therefore you should 'export' again each environment variable that
     you update.

'false'
     Don't expect 'false' to exit with status 1: in the native Bourne
     shell of Solaris 8, it exits with status 255.

'for'
     To loop over positional arguments, use:

          for arg
          do
            echo "$arg"
          done

     You may _not_ leave the 'do' on the same line as 'for', since some
     shells improperly grok:

          for arg; do
            echo "$arg"
          done

     If you want to explicitly refer to the positional arguments, given
     the '$@' bug (*note Shell Substitutions::), use:

          for arg in ${1+"$@"}; do
            echo "$arg"
          done

'if'
     Using '!' is not portable.  Instead of:

          if ! cmp -s file file.new; then
            mv file.new file
          fi

     use:

          if cmp -s file file.new; then :; else
            mv file.new file
          fi

     There are shells that do not reset the exit status from an 'if':

          $ if (exit 42); then true; fi; echo $?
          42

     whereas a proper shell should have printed '0'.  This is especially
     bad in Makefiles since it produces false failures.  This is why
     properly written Makefiles, such as Automake's, have such hairy
     constructs:

          if test -f "$file"; then
            install "$file" "$dest"
          else
            :
          fi

'set'
     This builtin faces the usual problem with arguments starting with a
     dash.  Modern shells such as Bash or Zsh understand '--' to specify
     the end of the options (any argument after '--' is a parameters,
     even '-x' for instance), but most shells simply stop the option
     processing as soon as a non-option argument is found.  Therefore,
     use 'dummy' or simply 'x' to end the option processing, and use
     'shift' to pop it out:

          set x $my_list; shift

'shift'
     Not only is 'shift'ing a bad idea when there is nothing left to
     shift, but in addition it is not portable: the shell of MIPS
     RISC/OS 4.52 refuses to do it.

'test'
     The 'test' program is the way to perform many file and string
     tests.  It is often invoked by the alternate name '[', but using
     that name in Autoconf code is asking for trouble since it is an M4
     quote character.

     If you need to make multiple checks using 'test', combine them with
     the shell operators '&&' and '||' instead of using the 'test'
     operators '-a' and '-o'.  On System V, the precedence of '-a' and
     '-o' is wrong relative to the unary operators; consequently, POSIX
     does not specify them, so using them is nonportable.  If you
     combine '&&' and '||' in the same statement, keep in mind that they
     have equal precedence.

     You may use '!' with 'test', but not with 'if': 'test ! -r foo ||
     exit 1'.

'test' (files)
     To enable 'configure' scripts to support cross-compilation, they
     shouldn't do anything that tests features of the build system
     instead of the host system.  But occasionally you may find it
     necessary to check whether some arbitrary file exists.  To do so,
     use 'test -f' or 'test -r'.  Do not use 'test -x', because 4.3BSD
     does not have it.  Do not use 'test -e' either, because Solaris 2.5
     does not have it.

'test' (strings)
     Avoid 'test "STRING"', in particular if STRING might start with a
     dash, since 'test' might interpret its argument as an option (e.g.,
     'STRING = "-n"').

     Contrary to a common belief, 'test -n STRING' and 'test -z STRING'
     *are* portable, nevertheless many shells (such as Solaris 2.5, AIX
     3.2, UNICOS 10.0.0.6, Digital Unix 4 etc.)  have bizarre precedence
     and may be confused if STRING looks like an operator:

          $ test -n =
          test: argument expected

     If there are risks, use 'test "xSTRING" = x' or 'test "xSTRING" !=
     x' instead.

     It is frequent to find variations of the following idiom:

          test -n "`echo $ac_feature | sed 's/[-a-zA-Z0-9_]//g'`" &&
            ACTION

     to take an action when a token matches a given pattern.  Such
     constructs should always be avoided by using:

          echo "$ac_feature" | grep '[^-a-zA-Z0-9_]' >/dev/null 2>&1 &&
            ACTION

     Use 'case' where possible since it is faster, being a shell
     builtin:

          case $ac_feature in
            *[!-a-zA-Z0-9_]*) ACTION;;
          esac

     Alas, negated character classes are probably not portable, although
     no shell is known to not support the POSIX.2 syntax '[!...]' (when
     in interactive mode, 'zsh' is confused by the '[!...]' syntax and
     looks for an event in its history because of '!').  Many shells do
     not support the alternative syntax '[^...]' (Solaris, Digital Unix,
     etc.).

     One solution can be:

          expr "$ac_feature" : '.*[^-a-zA-Z0-9_]' >/dev/null &&
            ACTION

     or better yet

          expr "x$ac_feature" : '.*[^-a-zA-Z0-9_]' >/dev/null &&
            ACTION

     'expr "XFOO" : "XBAR"' is more robust than 'echo "XFOO" | grep
     "^XBAR"', because it avoids problems when 'FOO' contains
     backslashes.

'trap'
     It is safe to trap at least the signals 1, 2, 13 and 15.  You can
     also trap 0, i.e., have the 'trap' run when the script ends (either
     via an explicit 'exit', or the end of the script).

     Although POSIX is not absolutely clear on this point, it is widely
     admitted that when entering the trap '$?' should be set to the exit
     status of the last command run before the trap.  The ambiguity can
     be summarized as: "when the trap is launched by an 'exit', what is
     the _last_ command run: that before 'exit', or 'exit' itself?"

     Bash considers 'exit' to be the last command, while Zsh and Solaris
     8 'sh' consider that when the trap is run it is _still_ in the
     'exit', hence it is the previous exit status that the trap
     receives:

          $ cat trap.sh
          trap 'echo $?' 0
          (exit 42); exit 0
          $ zsh trap.sh
          42
          $ bash trap.sh
          0

     The portable solution is then simple: when you want to 'exit 42',
     run '(exit 42); exit 42', the first 'exit' being used to set the
     exit status to 42 for Zsh, and the second to trigger the trap and
     pass 42 as exit status for Bash.

     The shell in FreeBSD 4.0 has the following bug: '$?' is reset to 0
     by empty lines if the code is inside 'trap'.

          $ trap 'false

          echo $?' 0
          $ exit
          0

     Fortunately, this bug only affects 'trap'.

'true'
     Don't worry: as far as we know 'true' is portable.  Nevertheless,
     it's not always a builtin (e.g., Bash 1.x), and the portable shell
     community tends to prefer using ':'.  This has a funny side effect:
     when asked whether 'false' is more portable than 'true' Alexandre
     Oliva answered:

          In a sense, yes, because if it doesn't exist, the shell will
          produce an exit status of failure, which is correct for
          'false', but not for 'true'.

'unset'
     You cannot assume the support of 'unset', nevertheless, because it
     is extremely useful to disable embarrassing variables such as
     'CDPATH' or 'LANG', you can test for its existence and use it
     _provided_ you give a neutralizing value when 'unset' is not
     supported:

          if (unset FOO) >/dev/null 2>&1; then
            unset=unset
          else
            unset=false
          fi
          $unset CDPATH || CDPATH=:

     *Note Special Shell Variables::, for some neutralizing values.
     Also, see *note Limitations of Builtins::, documentation of
     'export', for the case of environment variables.


File: autoconf.info,  Node: Limitations of Usual Tools,  Next: Limitations of Make,  Prev: Limitations of Builtins,  Up: Portable Shell

10.9 Limitations of Usual Tools
===============================

The small set of tools you can expect to find on any machine can still
include some limitations you should be aware of.

'awk'
     Don't leave white spaces before the parentheses in user functions
     calls, GNU awk will reject it:

          $ gawk 'function die () { print "Aaaaarg!"  }
                  BEGIN { die () }'
          gawk: cmd. line:2:         BEGIN { die () }
          gawk: cmd. line:2:                      ^ parse error
          $ gawk 'function die () { print "Aaaaarg!"  }
                  BEGIN { die() }'
          Aaaaarg!

     If you want your program to be deterministic, don't depend on 'for'
     on arrays:

          $ cat for.awk
          END {
            arr["foo"] = 1
            arr["bar"] = 1
            for (i in arr)
              print i
          }
          $ gawk -f for.awk </dev/null
          foo
          bar
          $ nawk -f for.awk </dev/null
          bar
          foo

     Some AWK, such as HPUX 11.0's native one, have regex engines
     fragile to inner anchors:

          $ echo xfoo | $AWK '/foo|^bar/ { print }'
          $ echo bar | $AWK '/foo|^bar/ { print }'
          bar
          $ echo xfoo | $AWK '/^bar|foo/ { print }'
          xfoo
          $ echo bar | $AWK '/^bar|foo/ { print }'
          bar

     Either do not depend on such patterns (i.e., use '/^(.*foo|bar)/',
     or use a simple test to reject such AWK.

'cat'
     Don't rely on any option.  The option '-v', which displays
     non-printing characters, _seems_ portable, though.

'cc'
     When a compilation such as 'cc foo.c -o foo' fails, some compilers
     (such as CDS on Reliant UNIX) leave a 'foo.o'.

'cmp'
     'cmp' performs a raw data comparison of two files, while 'diff'
     compares two text files.  Therefore, if you might compare DOS
     files, even if only checking whether two files are different, use
     'diff' to avoid spurious differences due to differences of newline
     encoding.

'cp'
     SunOS 'cp' does not support '-f', although its 'mv' does.  It's
     possible to deduce why 'mv' and 'cp' are different with respect to
     '-f'.  'mv' prompts by default before overwriting a read-only file.
     'cp' does not.  Therefore, 'mv' requires a '-f' option, but 'cp'
     does not.  'mv' and 'cp' behave differently with respect to
     read-only files because the simplest form of 'cp' cannot overwrite
     a read-only file, but the simplest form of 'mv' can.  This is
     because 'cp' opens the target for write access, whereas 'mv' simply
     calls 'link' (or, in newer systems, 'rename').

'diff'
     Option '-u' is nonportable.

     Some implementations, such as Tru64's, fail when comparing to
     '/dev/null'.  Use an empty file instead.

'dirname'
     Not all hosts have 'dirname', but it is reasonably easy to emulate,
     e.g.:

          dir=`expr "x$file" : 'x\(.*\)/[^/]*' \|
                    '.'      : '.'

     But there are a few subtilities, e.g., under UN*X, should '//1'
     give '/'?  Paul Eggert answers:

          No, under some older flavors of Unix, leading '//' is a
          special path name: it refers to a "super-root" and is used to
          access other machines' files.  Leading '///', '////', etc.
          are equivalent to '/'; but leading '//' is special.  I think
          this tradition started with Apollo Domain/OS, an OS that is
          still in use on some older hosts.

          POSIX.2 allows but does not require the special treatment for
          '//'.  It says that the behavior of dirname on path names of
          the form '//([^/]+/*)?' is implementation defined.  In these
          cases, GNU 'dirname' returns '/', but it's more portable to
          return '//' as this works even on those older flavors of Unix.

          I have heard rumors that this special treatment of '//' may be
          dropped in future versions of POSIX, but for now it's still
          the standard.

'egrep'
     The empty alternative is not portable, use '?' instead.  For
     instance with Digital Unix v5.0:

          > printf "foo\n|foo\n" | egrep '^(|foo|bar)$'
          |foo
          > printf "bar\nbar|\n" | egrep '^(foo|bar|)$'
          bar|
          > printf "foo\nfoo|\n|bar\nbar\n" | egrep '^(foo||bar)$'
          foo
          |bar

     'egrep' also suffers the limitations of 'grep'.

'expr'
     No 'expr' keyword starts with 'x', so use 'expr x"WORD" : 'xREGEX''
     to keep 'expr' from misinterpreting WORD.

     Don't use 'length', 'substr', 'match' and 'index'.

'expr' ('|')
     You can use '|'.  Although POSIX does require that 'expr ''' return
     the empty string, it does not specify the result when you '|'
     together the empty string (or zero) with the empty string.  For
     example:

          expr '' \| ''

     GNU/Linux and POSIX.2-1992 return the empty string for this case,
     but traditional Unix returns '0' (Solaris is one such example).  In
     the latest POSIX draft, the specification has been changed to match
     traditional Unix's behavior (which is bizarre, but it's too late to
     fix this).  Please note that the same problem does arise when the
     empty string results from a computation, as in:

          expr bar : foo \| foo : bar

     Avoid this portability problem by avoiding the empty string.

'expr' (':')
     Don't use '\?', '\+' and '\|' in patterns, they are not supported
     on Solaris.

     The POSIX.2-1992 standard is ambiguous as to whether 'expr a : b'
     (and 'expr 'a' : '\(b\)'') output '0' or the empty string.  In
     practice, it outputs the empty string on most platforms, but
     portable scripts should not assume this.  For instance, the QNX
     4.25 native 'expr' returns '0'.

     You may believe that one means to get a uniform behavior would be
     to use the empty string as a default value:

          expr a : b \| ''

     unfortunately this behaves exactly as the original expression, see
     the ''expr' (':')' entry for more information.

     Older 'expr' implementations (e.g.  SunOS 4 'expr' and Solaris 8
     '/usr/ucb/expr') have a silly length limit that causes 'expr' to
     fail if the matched substring is longer than 120 bytes.  In this
     case, you might want to fall back on 'echo|sed' if 'expr' fails.

     Don't leave, there is some more!

     The QNX 4.25 'expr', in addition of preferring '0' to the empty
     string, has a funny behavior in its exit status: it's always 1 when
     parentheses are used!

          $ val=`expr 'a' : 'a'`; echo "$?: $val"
          0: 1
          $ val=`expr 'a' : 'b'`; echo "$?: $val"
          1: 0

          $ val=`expr 'a' : '\(a\)'`; echo "?: $val"
          1: a
          $ val=`expr 'a' : '\(b\)'`; echo "?: $val"
          1: 0

     In practice this can be a big problem if you are ready to catch
     failures of 'expr' programs with some other method (such as using
     'sed'), since you may get twice the result.  For instance

          $ expr 'a' : '\(a\)' || echo 'a' | sed 's/^\(a\)$/\1/'

     will output 'a' on most hosts, but 'aa' on QNX 4.25.  A simple work
     around consists in testing 'expr' and use a variable set to 'expr'
     or to 'false' according to the result.

'find'
     The option '-maxdepth' seems to be GNU specific.  Tru64 v5.1,
     NetBSD 1.5 and Solaris 2.5 'find' commands do not understand it.

'grep'
     Don't use 'grep -s' to suppress output, because 'grep -s' on System
     V does not suppress output, only error messages.  Instead, redirect
     the standard output and standard error (in case the file doesn't
     exist) of 'grep' to '/dev/null'.  Check the exit status of 'grep'
     to determine whether it found a match.

     Don't use multiple regexps with '-e', as some 'grep' will only
     honor the last pattern (eg., IRIX 6.5 and Solaris 2.5.1).  Anyway,
     Stardent Vistra SVR4 'grep' lacks '-e'... Instead, use alternation
     and 'egrep'.

'ln'
     Don't rely on 'ln' having a '-f' option.  Symbolic links are not
     available on old systems, use 'ln' as a fall back.

     For versions of the DJGPP before 2.04, 'ln' emulates soft links for
     executables by generating a stub that in turn calls the real
     program.  This feature also works with nonexistent files like in
     the Unix spec.  So 'ln -s file link' will generate 'link.exe',
     which will attempt to call 'file.exe' if run.  But this feature
     only works for executables, so 'cp -p' is used instead for these
     systems.  DJGPP versions 2.04 and later have full symlink support.

'mv'
     The only portable options are '-f' and '-i'.

     Moving individual files between file systems is portable (it was in
     V6), but it is not always atomic: when doing 'mv new existing',
     there's a critical section where neither the old nor the new
     version of 'existing' actually exists.

     Moving directories across mount points is not portable, use 'cp'
     and 'rm'.

'sed'
     Patterns should not include the separator (unless escaped), even as
     part of a character class.  In conformance with POSIX, the Cray
     'sed' will reject 's/[^/]*$//': use 's,[^/]*$,,'.

     Sed scripts should not use branch labels longer than 8 characters
     and should not contain comments.

     Don't include extra ';', as some 'sed', such as NetBSD 1.4.2's, try
     to interpret the second as a command:

          $ echo a | sed 's/x/x/;;s/x/x/'
          sed: 1: "s/x/x/;;s/x/x/": invalid command code ;

     Input should have reasonably long lines, since some 'sed' have an
     input buffer limited to 4000 bytes.

     Alternation, '\|', is common but not portable.  Anchors ('^' and
     '$') inside groups are not portable.

     Nested groups are extremely portable, but there is at least one
     'sed' (System V/68 Base Operating System R3V7.1) that does not
     support it.

     Of course the option '-e' is portable, but it is not needed.  No
     valid Sed program can start with a dash, so it does not help
     disambiguating.  Its sole usefulness is helping enforcing indenting
     as in:

          sed -e INSTRUCTION-1 \
              -e INSTRUCTION-2

     as opposed to

          sed INSTRUCTION-1;INSTRUCTION-2

     Contrary to yet another urban legend, you may portably use '&' in
     the replacement part of the 's' command to mean "what was matched".

'sed' ('t')
     Some old systems have 'sed' that "forget" to reset their 't' flag
     when starting a new cycle.  For instance on MIPS RISC/OS, and on
     IRIX 5.3, if you run the following 'sed' script (the line numbers
     are not actual part of the texts):

          s/keep me/kept/g  # a
          t end             # b
          s/.*/deleted/g    # c
          : end             # d

     on

          delete me         # 1
          delete me         # 2
          keep me           # 3
          delete me         # 4

     you get

          deleted
          delete me
          kept
          deleted

     instead of

          deleted
          deleted
          kept
          deleted

     Why?  When processing 1, a matches, therefore sets the t flag, b
     jumps to d, and the output is produced.  When processing line 2,
     the t flag is still set (this is the bug).  Line a fails to match,
     but 'sed' is not supposed to clear the t flag when a substitution
     fails.  Line b sees that the flag is set, therefore it clears it,
     and jumps to d, hence you get 'delete me' instead of 'deleted'.
     When processing 3 t is clear, a matches, so the flag is set, hence
     b clears the flags and jumps.  Finally, since the flag is clear, 4
     is processed properly.

     There are two things one should remind about 't' in 'sed'.
     Firstly, always remember that 't' jumps if _some_ substitution
     succeeded, not only the immediately preceding substitution,
     therefore, always use a fake 't clear; : clear' to reset the t flag
     where indeed.

     Secondly, you cannot rely on 'sed' to clear the flag at each new
     cycle.

     One portable implementation of the script above is:

          t clear
          : clear
          s/keep me/kept/g
          t end
          s/.*/deleted/g
          : end

'touch'
     On some old BSD systems, 'touch' or any command that results in an
     empty file does not update the timestamps, so use a command like
     'echo' as a workaround.

     GNU 'touch' 3.16r (and presumably all before that) fails to work on
     SunOS 4.1.3 when the empty file is on an NFS-mounted 4.2 volume.


File: autoconf.info,  Node: Limitations of Make,  Prev: Limitations of Usual Tools,  Up: Portable Shell

10.10 Limitations of Make
=========================

Make itself suffers a great number of limitations, only a few of which
being listed here.  First of all, remember that since commands are
executed by the shell, all its weaknesses are inherited...

Leading underscore in macro names
     Some Make don't support leading underscores in macro names, such as
     on NEWS-OS 4.2R.

          $ cat Makefile
          _am_include = #
          _am_quote =
          all:; @echo this is test

          % make
          Make: Must be a separator on rules line 2.  Stop.

          $ cat Makefile2
          am_include = #
          am_quote =
          all:; @echo this is test

          $ make -f Makefile2
          this is test

'VPATH'
     Don't use it!  For instance any assignment to 'VPATH' causes Sun
     'make' to only execute the first set of double-colon rules.


File: autoconf.info,  Node: Manual Configuration,  Next: Site Configuration,  Prev: Portable Shell,  Up: Top

11 Manual Configuration
***********************

A few kinds of features can't be guessed automatically by running test
programs.  For example, the details of the object-file format, or
special options that need to be passed to the compiler or linker.  You
can check for such features using ad-hoc means, such as having
'configure' check the output of the 'uname' program, or looking for
libraries that are unique to particular systems.  However, Autoconf
provides a uniform method for handling unguessable features.

* Menu:

* Specifying Names::            Specifying the system type
* Canonicalizing::              Getting the canonical system type
* Using System Type::           What to do with the system type


File: autoconf.info,  Node: Specifying Names,  Next: Canonicalizing,  Prev: Manual Configuration,  Up: Manual Configuration

11.1 Specifying the System Type
===============================

Like other GNU 'configure' scripts, Autoconf-generated 'configure'
scripts can make decisions based on a canonical name for the system
type, which has the form: 'CPU-VENDOR-OS', where OS can be 'SYSTEM' or
'KERNEL-SYSTEM'

   'configure' can usually guess the canonical name for the type of
system it's running on.  To do so it runs a script called
'config.guess', which infers the name using the 'uname' command or
symbols predefined by the C preprocessor.

   Alternately, the user can specify the system type with command line
arguments to 'configure'.  Doing so is necessary when cross-compiling.
In the most complex case of cross-compiling, three system types are
involved.  The options to specify them are(1):

'--build=BUILD-TYPE'
     the type of system on which the package is being configured and
     compiled.

'--host=HOST-TYPE'
     the type of system on which the package will run.

'--target=TARGET-TYPE'
     the type of system for which any compiler tools in the package will
     produce code (rarely needed).  By default, it is the same as host.

   They all default to the result of running 'config.guess', unless you
specify either '--build' or '--host'.  In this case, the default becomes
the system type you specified.  If you specify both, and they're
different, 'configure' will enter cross compilation mode, so it won't
run any tests that require execution.

   Hint: if you mean to override the result of 'config.guess', prefer
'--build' over '--host'.  In the future, '--host' will not override the
name of the build system type.  Also, if you specify '--host', but not
'--build', when 'configure' performs the first compiler test it will try
to run an executable produced by the compiler.  If the execution fails,
it will enter cross-compilation mode.  Note, however, that it won't
guess the build-system type, since this may require running test
programs.  Moreover, by the time the compiler test is performed, it may
be too late to modify the build-system type: other tests may have
already been performed.  Therefore, whenever you specify '--host', be
sure to specify '--build' too.

     ./configure --build=i686-pc-linux-gnu --host=m68k-coff

will enter cross-compilation mode, but 'configure' will fail if it can't
run the code generated by the specified compiler if you configure as
follows:

     ./configure CC=m68k-coff-gcc

   'configure' recognizes short aliases for many system types; for
example, 'decstation' can be used instead of 'mips-dec-ultrix4.2'.
'configure' runs a script called 'config.sub' to canonicalize system
type aliases.

   ---------- Footnotes ----------

   (1) For backward compatibility, 'configure' will accept a system type
as an option by itself.  Such an option will override the defaults for
build, host and target system types.  The following configure statement
will configure a cross toolchain that will run on NetBSD/alpha but
generate code for GNU Hurd/sparc, which is also the build platform.

     ./configure --host=alpha-netbsd sparc-gnu


File: autoconf.info,  Node: Canonicalizing,  Next: Using System Type,  Prev: Specifying Names,  Up: Manual Configuration

11.2 Getting the Canonical System Type
======================================

The following macros make the system type available to 'configure'
scripts.

   The variables 'build_alias', 'host_alias', and 'target_alias' are
always exactly the arguments of '--build', '--host', and '--target'; in
particular, they are left empty if the user did not use them, even if
the corresponding 'AC_CANONICAL' macro was run.  Any configure script
may use these variables anywhere.  These are the variables that should
be used when in interaction with the user.

   If you need to recognize some special environments based on their
system type, run the following macros to get canonical system names.
These variables are not set before the macro call.

   If you use these macros, you must distribute 'config.guess' and
'config.sub' along with your source code.  *Note Output::, for
information about the 'AC_CONFIG_AUX_DIR' macro which you can use to
control in which directory 'configure' looks for those scripts.

 -- Macro: AC_CANONICAL_BUILD
     Compute the canonical build-system type variable, 'build', and its
     three individual parts 'build_cpu', 'build_vendor', and 'build_os'.

     If '--build' was specified, then 'build' is the canonicalization of
     'build_alias' by 'config.sub', otherwise it is determined by the
     shell script 'config.guess'.

 -- Macro: AC_CANONICAL_HOST
     Compute the canonical host-system type variable, 'host', and its
     three individual parts 'host_cpu', 'host_vendor', and 'host_os'.

     If '--host' was specified, then 'host' is the canonicalization of
     'host_alias' by 'config.sub', otherwise it defaults to 'build'.

     For temporary backward-compatibility, when '--host' is specified by
     '--build' isn't, the build system will be assumed to be the same as
     '--host', and 'build_alias' will be set to that value.  Eventually,
     this historically incorrect behavior will go away.

 -- Macro: AC_CANONICAL_TARGET
     Compute the canonical target-system type variable, 'target', and
     its three individual parts 'target_cpu', 'target_vendor', and
     'target_os'.

     If '--target' was specified, then 'target' is the canonicalization
     of 'target_alias' by 'config.sub', otherwise it defaults to 'host'.


File: autoconf.info,  Node: Using System Type,  Prev: Canonicalizing,  Up: Manual Configuration

11.3 Using the System Type
==========================

How do you use a canonical system type?  Usually, you use it in one or
more 'case' statements in 'configure.ac' to select system-specific C
files.  Then, using 'AC_CONFIG_LINKS', link those files which have names
based on the system name, to generic names, such as 'host.h' or
'target.c' (*note Configuration Links::).  The 'case' statement patterns
can use shell wild cards to group several cases together, like in this
fragment:

     case "$target" in
     i386-*-mach* | i386-*-gnu*)
                  obj_format=aout emulation=mach bfd_gas=yes ;;
     i960-*-bout) obj_format=bout ;;
     esac

and in 'configure.ac', use:

     AC_CONFIG_LINKS(host.h:config/$machine.h
                     object.h:config/$obj_format.h)

   You can also use the host system type to find cross-compilation
tools.  *Note Generic Programs::, for information about the
'AC_CHECK_TOOL' macro which does that.


File: autoconf.info,  Node: Site Configuration,  Next: Running configure scripts,  Prev: Manual Configuration,  Up: Top

12 Site Configuration
*********************

'configure' scripts support several kinds of local configuration
decisions.  There are ways for users to specify where external software
packages are, include or exclude optional features, install programs
under modified names, and set default values for 'configure' options.

* Menu:

* External Software::           Working with other optional software
* Package Options::             Selecting optional features
* Pretty Help Strings::         Formatting help string
* Site Details::                Configuring site details
* Transforming Names::          Changing program names when installing
* Site Defaults::               Giving 'configure' local defaults


File: autoconf.info,  Node: External Software,  Next: Package Options,  Prev: Site Configuration,  Up: Site Configuration

12.1 Working With External Software
===================================

Some packages require, or can optionally use, other software packages
that are already installed.  The user can give 'configure' command line
options to specify which such external software to use.  The options
have one of these forms:

     --with-PACKAGE=[ARG]
     --without-PACKAGE

   For example, '--with-gnu-ld' means work with the GNU linker instead
of some other linker.  '--with-x' means work with The X Window System.

   The user can give an argument by following the package name with '='
and the argument.  Giving an argument of 'no' is for packages that are
used by default; it says to _not_ use the package.  An argument that is
neither 'yes' nor 'no' could include a name or number of a version of
the other package, to specify more precisely which other package this
program is supposed to work with.  If no argument is given, it defaults
to 'yes'.  '--without-PACKAGE' is equivalent to '--with-PACKAGE=no'.

   'configure' scripts do not complain about '--with-PACKAGE' options
that they do not support.  This behavior permits configuring a source
tree containing multiple packages with a top-level 'configure' script
when the packages support different options, without spurious error
messages about options that some of the packages support.  An
unfortunate side effect is that option spelling errors are not
diagnosed.  No better approach to this problem has been suggested so
far.

   For each external software package that may be used, 'configure.ac'
should call 'AC_ARG_WITH' to detect whether the 'configure' user asked
to use it.  Whether each package is used or not by default, and which
arguments are valid, is up to you.

 -- Macro: AC_ARG_WITH (PACKAGE, HELP-STRING, [ACTION-IF-GIVEN],
          [ACTION-IF-NOT-GIVEN])
     If the user gave 'configure' the option '--with-PACKAGE' or
     '--without-PACKAGE', run shell commands ACTION-IF-GIVEN.  If
     neither option was given, run shell commands ACTION-IF-NOT-GIVEN.
     The name PACKAGE indicates another software package that this
     program should work with.  It should consist only of alphanumeric
     characters and dashes.

     The option's argument is available to the shell commands
     ACTION-IF-GIVEN in the shell variable 'withval', which is actually
     just the value of the shell variable 'with_PACKAGE', with any '-'
     characters changed into '_'.  You may use that variable instead, if
     you wish.

     The argument HELP-STRING is a description of the option that looks
     like this:
            --with-readline         support fancy command line editing

     HELP-STRING may be more than one line long, if more detail is
     needed.  Just make sure the columns line up in 'configure --help'.
     Avoid tabs in the help string.  You'll need to enclose it in '['
     and ']' in order to produce the leading spaces.

     You should format your HELP-STRING with the macro 'AC_HELP_STRING'
     (*note Pretty Help Strings::).

 -- Macro: AC_WITH (PACKAGE, ACTION-IF-GIVEN, [ACTION-IF-NOT-GIVEN])
     This is an obsolete version of 'AC_ARG_WITH' that does not support
     providing a help string.


File: autoconf.info,  Node: Package Options,  Next: Pretty Help Strings,  Prev: External Software,  Up: Site Configuration

12.2 Choosing Package Options
=============================

If a software package has optional compile-time features, the user can
give 'configure' command line options to specify whether to compile
them.  The options have one of these forms:

     --enable-FEATURE=[ARG]
     --disable-FEATURE

   These options allow users to choose which optional features to build
and install.  '--enable-FEATURE' options should never make a feature
behave differently or cause one feature to replace another.  They should
only cause parts of the program to be built rather than left out.

   The user can give an argument by following the feature name with '='
and the argument.  Giving an argument of 'no' requests that the feature
_not_ be made available.  A feature with an argument looks like
'--enable-debug=stabs'.  If no argument is given, it defaults to 'yes'.
'--disable-FEATURE' is equivalent to '--enable-FEATURE=no'.

   'configure' scripts do not complain about '--enable-FEATURE' options
that they do not support.  This behavior permits configuring a source
tree containing multiple packages with a top-level 'configure' script
when the packages support different options, without spurious error
messages about options that some of the packages support.  An
unfortunate side effect is that option spelling errors are not
diagnosed.  No better approach to this problem has been suggested so
far.

   For each optional feature, 'configure.ac' should call 'AC_ARG_ENABLE'
to detect whether the 'configure' user asked to include it.  Whether
each feature is included or not by default, and which arguments are
valid, is up to you.

 -- Macro: AC_ARG_ENABLE (FEATURE, HELP-STRING, [ACTION-IF-GIVEN],
          [ACTION-IF-NOT-GIVEN])
     If the user gave 'configure' the option '--enable-FEATURE' or
     '--disable-FEATURE', run shell commands ACTION-IF-GIVEN.  If
     neither option was given, run shell commands ACTION-IF-NOT-GIVEN.
     The name FEATURE indicates an optional user-level facility.  It
     should consist only of alphanumeric characters and dashes.

     The option's argument is available to the shell commands
     ACTION-IF-GIVEN in the shell variable 'enableval', which is
     actually just the value of the shell variable 'enable_FEATURE',
     with any '-' characters changed into '_'.  You may use that
     variable instead, if you wish.  The HELP-STRING argument is like
     that of 'AC_ARG_WITH' (*note External Software::).

     You should format your HELP-STRING with the macro 'AC_HELP_STRING'
     (*note Pretty Help Strings::).

 -- Macro: AC_ENABLE (FEATURE, ACTION-IF-GIVEN, [ACTION-IF-NOT-GIVEN])
     This is an obsolete version of 'AC_ARG_ENABLE' that does not
     support providing a help string.


File: autoconf.info,  Node: Pretty Help Strings,  Next: Site Details,  Prev: Package Options,  Up: Site Configuration

12.3 Making Your Help Strings Look Pretty
=========================================

Properly formatting the 'help strings' which are used in 'AC_ARG_WITH'
(*note External Software::) and 'AC_ARG_ENABLE' (*note Package
Options::) can be challenging.  Specifically, you want your own 'help
strings' to line up in the appropriate columns of 'configure --help'
just like the standard Autoconf 'help strings' do.  This is the purpose
of the 'AC_HELP_STRING' macro.

 -- Macro: AC_HELP_STRING (LEFT-HAND-SIDE, RIGHT-HAND-SIDE)

     Expands into an help string that looks pretty when the user
     executes 'configure --help'.  It is typically used in 'AC_ARG_WITH'
     (*note External Software::) or 'AC_ARG_ENABLE' (*note Package
     Options::).  The following example will make this clearer.

          AC_DEFUN(TEST_MACRO,
          [AC_ARG_WITH(foo,
                       AC_HELP_STRING([--with-foo],
                                      [use foo (default is NO)]),
                       ac_cv_use_foo=$withval, ac_cv_use_foo=no),
          AC_CACHE_CHECK(whether to use foo,
                         ac_cv_use_foo, ac_cv_use_foo=no)])

     Please note that the call to 'AC_HELP_STRING' is *unquoted*.  Then
     the last few lines of 'configure --help' will appear like this:

          --enable and --with options recognized:
            --with-foo              use foo (default is NO)

     The 'AC_HELP_STRING' macro is particularly helpful when the
     LEFT-HAND-SIDE and/or RIGHT-HAND-SIDE are composed of macro
     arguments, as shown in the following example.

          AC_DEFUN(MY_ARG_WITH,
          [AC_ARG_WITH([$1],
                       AC_HELP_STRING([--with-$1], [use $1 (default is $2)]),
                       ac_cv_use_$1=$withval, ac_cv_use_$1=no),
          AC_CACHE_CHECK(whether to use $1, ac_cv_use_$1, ac_cv_use_$1=$2)])


File: autoconf.info,  Node: Site Details,  Next: Transforming Names,  Prev: Pretty Help Strings,  Up: Site Configuration

12.4 Configuring Site Details
=============================

Some software packages require complex site-specific information.  Some
examples are host names to use for certain services, company names, and
email addresses to contact.  Since some configuration scripts generated
by Metaconfig ask for such information interactively, people sometimes
wonder how to get that information in Autoconf-generated configuration
scripts, which aren't interactive.

   Such site configuration information should be put in a file that is
edited _only by users_, not by programs.  The location of the file can
either be based on the 'prefix' variable, or be a standard location such
as the user's home directory.  It could even be specified by an
environment variable.  The programs should examine that file at run
time, rather than at compile time.  Run time configuration is more
convenient for users and makes the configuration process simpler than
getting the information while configuring.  *Note Variables for
Installation Directories: (standards)Directory Variables, for more
information on where to put data files.


File: autoconf.info,  Node: Transforming Names,  Next: Site Defaults,  Prev: Site Details,  Up: Site Configuration

12.5 Transforming Program Names When Installing
===============================================

Autoconf supports changing the names of programs when installing them.
In order to use these transformations, 'configure.ac' must call the
macro 'AC_ARG_PROGRAM'.

 -- Macro: AC_ARG_PROGRAM
     Place in output variable 'program_transform_name' a sequence of
     'sed' commands for changing the names of installed programs.

     If any of the options described below are given to 'configure',
     program names are transformed accordingly.  Otherwise, if
     'AC_CANONICAL_TARGET' has been called and a '--target' value is
     given that differs from the host type (specified with '--host'),
     the target type followed by a dash is used as a prefix.  Otherwise,
     no program name transformation is done.

* Menu:

* Transformation Options::      'configure' options to transform names
* Transformation Examples::     Sample uses of transforming names
* Transformation Rules::        'Makefile' uses of transforming names


File: autoconf.info,  Node: Transformation Options,  Next: Transformation Examples,  Prev: Transforming Names,  Up: Transforming Names

12.5.1 Transformation Options
-----------------------------

You can specify name transformations by giving 'configure' these command
line options:

'--program-prefix=PREFIX'
     prepend PREFIX to the names;

'--program-suffix=SUFFIX'
     append SUFFIX to the names;

'--program-transform-name=EXPRESSION'
     perform 'sed' substitution EXPRESSION on the names.


File: autoconf.info,  Node: Transformation Examples,  Next: Transformation Rules,  Prev: Transformation Options,  Up: Transforming Names

12.5.2 Transformation Examples
------------------------------

These transformations are useful with programs that can be part of a
cross-compilation development environment.  For example, a
cross-assembler running on a Sun 4 configured with
'--target=i960-vxworks' is normally installed as 'i960-vxworks-as',
rather than 'as', which could be confused with a native Sun 4 assembler.

   You can force a program name to begin with 'g', if you don't want GNU
programs installed on your system to shadow other programs with the same
name.  For example, if you configure GNU 'diff' with
'--program-prefix=g', then when you run 'make install' it is installed
as '/usr/local/bin/gdiff'.

   As a more sophisticated example, you could use

     --program-transform-name='s/^/g/; s/^gg/g/; s/^gless/less/'

   to prepend 'g' to most of the program names in a source tree,
excepting those like 'gdb' that already have one and those like 'less'
and 'lesskey' that aren't GNU programs.  (That is assuming that you have
a source tree containing those programs that is set up to use this
feature.)

   One way to install multiple versions of some programs simultaneously
is to append a version number to the name of one or both.  For example,
if you want to keep Autoconf version 1 around for awhile, you can
configure Autoconf version 2 using '--program-suffix=2' to install the
programs as '/usr/local/bin/autoconf2', '/usr/local/bin/autoheader2',
etc.  Nevertheless, pay attention that only the binaries are renamed,
therefore you'd have problems with the library files which might
overlap.


File: autoconf.info,  Node: Transformation Rules,  Prev: Transformation Examples,  Up: Transforming Names

12.5.3 Transformation Rules
---------------------------

Here is how to use the variable 'program_transform_name' in a
'Makefile.in':

     transform = @program_transform_name@
     install: all
             $(INSTALL_PROGRAM) myprog $(bindir)/`echo myprog | \
                                                    sed '$(transform)'`

     uninstall:
             rm -f $(bindir)/`echo myprog | sed '$(transform)'`

If you have more than one program to install, you can do it in a loop:

     PROGRAMS = cp ls rm
     install:
             for p in $(PROGRAMS); do \
               $(INSTALL_PROGRAM) $$p $(bindir)/`echo $$p | \
                                                   sed '$(transform)'`; \
             done

     uninstall:
             for p in $(PROGRAMS); do \
               rm -f $(bindir)/`echo $$p | sed '$(transform)'`; \
             done

   It is guaranteed that 'program_transform_name' is never empty, and
that there are no useless separators.  Therefore you may safely embed
'program_transform_name' within a sed program using ';':

     transform = @program_transform_name@
     transform_exe = s/$(EXEEXT)$$//;$(transform);s/$$/$(EXEEXT)/

   Whether to do the transformations on documentation files (Texinfo or
'man') is a tricky question; there seems to be no perfect answer, due to
the several reasons for name transforming.  Documentation is not usually
particular to a specific architecture, and Texinfo files do not conflict
with system documentation.  But they might conflict with earlier
versions of the same files, and 'man' pages sometimes do conflict with
system documentation.  As a compromise, it is probably best to do name
transformations on 'man' pages but not on Texinfo manuals.


File: autoconf.info,  Node: Site Defaults,  Prev: Transforming Names,  Up: Site Configuration

12.6 Setting Site Defaults
==========================

Autoconf-generated 'configure' scripts allow your site to provide
default values for some configuration values.  You do this by creating
site- and system-wide initialization files.

   If the environment variable 'CONFIG_SITE' is set, 'configure' uses
its value as the name of a shell script to read.  Otherwise, it reads
the shell script 'PREFIX/share/config.site' if it exists, then
'PREFIX/etc/config.site' if it exists.  Thus, settings in
machine-specific files override those in machine-independent ones in
case of conflict.

   Site files can be arbitrary shell scripts, but only certain kinds of
code are really appropriate to be in them.  Because 'configure' reads
any cache file after it has read any site files, a site file can define
a default cache file to be shared between all Autoconf-generated
'configure' scripts run on that system (*note Cache Files::).  If you
set a default cache file in a site file, it is a good idea to also set
the output variable 'CC' in that site file, because the cache file is
only valid for a particular compiler, but many systems have several
available.

   You can examine or override the value set by a command line option to
'configure' in a site file; options set shell variables that have the
same names as the options, with any dashes turned into underscores.  The
exceptions are that '--without-' and '--disable-' options are like
giving the corresponding '--with-' or '--enable-' option and the value
'no'.  Thus, '--cache-file=localcache' sets the variable 'cache_file' to
the value 'localcache'; '--enable-warnings=no' or '--disable-warnings'
sets the variable 'enable_warnings' to the value 'no'; '--prefix=/usr'
sets the variable 'prefix' to the value '/usr'; etc.

   Site files are also good places to set default values for other
output variables, such as 'CFLAGS', if you need to give them non-default
values: anything you would normally do, repetitively, on the command
line.  If you use non-default values for PREFIX or EXEC_PREFIX (wherever
you locate the site file), you can set them in the site file if you
specify it with the 'CONFIG_SITE' environment variable.

   You can set some cache values in the site file itself.  Doing this is
useful if you are cross-compiling, so it is impossible to check features
that require running a test program.  You could "prime the cache" by
setting those values correctly for that system in
'PREFIX/etc/config.site'.  To find out the names of the cache variables
you need to set, look for shell variables with '_cv_' in their names in
the affected 'configure' scripts, or in the Autoconf M4 source code for
those macros.

   The cache file is careful to not override any variables set in the
site files.  Similarly, you should not override command-line options in
the site files.  Your code should check that variables such as 'prefix'
and 'cache_file' have their default values (as set near the top of
'configure') before changing them.

   Here is a sample file '/usr/share/local/gnu/share/config.site'.  The
command 'configure --prefix=/usr/share/local/gnu' would read this file
(if 'CONFIG_SITE' is not set to a different file).

     # config.site for configure
     #
     # Change some defaults.
     test "$prefix" = NONE && prefix=/usr/share/local/gnu
     test "$exec_prefix" = NONE && exec_prefix=/usr/local/gnu
     test "$sharedstatedir" = '$prefix/com' && sharedstatedir=/var
     test "$localstatedir" = '$prefix/var' && localstatedir=/var

     # Give Autoconf 2.x generated configure scripts a shared default
     # cache file for feature test results, architecture-specific.
     if test "$cache_file" = /dev/null; then
       cache_file="$prefix/var/config.cache"
       # A cache file is only valid for one C compiler.
       CC=gcc
     fi


File: autoconf.info,  Node: Running configure scripts,  Next: config.status Invocation,  Prev: Site Configuration,  Up: Top

13 Running 'configure' Scripts
******************************

Below are instructions on how to configure a package that uses a
'configure' script, suitable for inclusion as an 'INSTALL' file in the
package.  A plain-text version of 'INSTALL' which you may use comes with
Autoconf.

* Menu:

* Basic Installation::          Instructions for typical cases
* Compilers and Options::       Selecting compilers and optimization
* Multiple Architectures::      Compiling for multiple architectures at once
* Installation Names::          Installing in different directories
* Optional Features::           Selecting optional features
* System Type::                 Specifying the system type
* Sharing Defaults::            Setting site-wide defaults for 'configure'
* Environment Variables::       Defining environment variables.
* configure Invocation::        Changing how 'configure' runs


File: autoconf.info,  Node: Basic Installation,  Next: Compilers and Options,  Up: Running configure scripts

13.1 Basic Installation
=======================

These are generic installation instructions.

   The 'configure' shell script attempts to guess correct values for
various system-dependent variables used during compilation.  It uses
those values to create a 'Makefile' in each directory of the package.
It may also create one or more '.h' files containing system-dependent
definitions.  Finally, it creates a shell script 'config.status' that
you can run in the future to recreate the current configuration, and a
file 'config.log' containing compiler output (useful mainly for
debugging 'configure').

   It can also use an optional file (typically called 'config.cache' and
enabled with '--cache-file=config.cache' or simply '-C') that saves the
results of its tests to speed up reconfiguring.  (Caching is disabled by
default to prevent problems with accidental use of stale cache files.)

   If you need to do unusual things to compile the package, please try
to figure out how 'configure' could check whether to do them, and mail
diffs or instructions to the address given in the 'README' so they can
be considered for the next release.  If you are using the cache, and at
some point 'config.cache' contains results you don't want to keep, you
may remove or edit it.

   The file 'configure.ac' (or 'configure.in') is used to create
'configure' by a program called 'autoconf'.  You only need
'configure.ac' if you want to change it or regenerate 'configure' using
a newer version of 'autoconf'.

The simplest way to compile this package is:

  1. 'cd' to the directory containing the package's source code and type
     './configure' to configure the package for your system.  If you're
     using 'csh' on an old version of System V, you might need to type
     'sh ./configure' instead to prevent 'csh' from trying to execute
     'configure' itself.

     Running 'configure' takes awhile.  While running, it prints some
     messages telling which features it is checking for.

  2. Type 'make' to compile the package.

  3. Optionally, type 'make check' to run any self-tests that come with
     the package.

  4. Type 'make install' to install the programs and any data files and
     documentation.

  5. You can remove the program binaries and object files from the
     source code directory by typing 'make clean'.  To also remove the
     files that 'configure' created (so you can compile the package for
     a different kind of computer), type 'make distclean'.  There is
     also a 'make maintainer-clean' target, but that is intended mainly
     for the package's developers.  If you use it, you may have to get
     all sorts of other programs in order to regenerate files that came
     with the distribution.


File: autoconf.info,  Node: Compilers and Options,  Next: Multiple Architectures,  Prev: Basic Installation,  Up: Running configure scripts

13.2 Compilers and Options
==========================

Some systems require unusual options for compilation or linking that the
'configure' script does not know about.  Run './configure --help' for
details on some of the pertinent environment variables.

   You can give 'configure' initial values for variables by setting them
in the environment.  You can do that on the command line like this:

     ./configure CC=c89 CFLAGS=-O2 LIBS=-lposix

   *Note Environment Variables::, for more details.


File: autoconf.info,  Node: Multiple Architectures,  Next: Installation Names,  Prev: Compilers and Options,  Up: Running configure scripts

13.3 Compiling For Multiple Architectures
=========================================

You can compile the package for more than one kind of computer at the
same time, by placing the object files for each architecture in their
own directory.  To do this, you must use a version of 'make' that
supports the 'VPATH' variable, such as GNU 'make'.  'cd' to the
directory where you want the object files and executables to go and run
the 'configure' script.  'configure' automatically checks for the source
code in the directory that 'configure' is in and in '..'.

   If you have to use a 'make' that does not support the 'VPATH'
variable, you have to compile the package for one architecture at a time
in the source code directory.  After you have installed the package for
one architecture, use 'make distclean' before reconfiguring for another
architecture.


File: autoconf.info,  Node: Installation Names,  Next: Optional Features,  Prev: Multiple Architectures,  Up: Running configure scripts

13.4 Installation Names
=======================

By default, 'make install' will install the package's files in
'/usr/local/bin', '/usr/local/man', etc.  You can specify an
installation prefix other than '/usr/local' by giving 'configure' the
option '--prefix=PATH'.

   You can specify separate installation prefixes for
architecture-specific files and architecture-independent files.  If you
give 'configure' the option '--exec-prefix=PATH', the package will use
PATH as the prefix for installing programs and libraries.  Documentation
and other data files will still use the regular prefix.

   In addition, if you use an unusual directory layout you can give
options like '--bindir=PATH' to specify different values for particular
kinds of files.  Run 'configure --help' for a list of the directories
you can set and what kinds of files go in them.

   If the package supports it, you can cause programs to be installed
with an extra prefix or suffix on their names by giving 'configure' the
option '--program-prefix=PREFIX' or '--program-suffix=SUFFIX'.


File: autoconf.info,  Node: Optional Features,  Next: System Type,  Prev: Installation Names,  Up: Running configure scripts

13.5 Optional Features
======================

Some packages pay attention to '--enable-FEATURE' options to
'configure', where FEATURE indicates an optional part of the package.
They may also pay attention to '--with-PACKAGE' options, where PACKAGE
is something like 'gnu-as' or 'x' (for the X Window System).  The
'README' should mention any '--enable-' and '--with-' options that the
package recognizes.

   For packages that use the X Window System, 'configure' can usually
find the X include and library files automatically, but if it doesn't,
you can use the 'configure' options '--x-includes=DIR' and
'--x-libraries=DIR' to specify their locations.


File: autoconf.info,  Node: System Type,  Next: Sharing Defaults,  Prev: Optional Features,  Up: Running configure scripts

13.6 Specifying the System Type
===============================

There may be some features 'configure' cannot figure out automatically,
but needs to determine by the type of host the package will run on.
Usually 'configure' can figure that out, but if it prints a message
saying it cannot guess the host type, give it the '--build=TYPE' option.
TYPE can either be a short name for the system type, such as 'sun4', or
a canonical name which has the form:

     CPU-COMPANY-SYSTEM

where SYSTEM can have one of these forms:

     OS
     KERNEL-OS

   See the file 'config.sub' for the possible values of each field.  If
'config.sub' isn't included in this package, then this package doesn't
need to know the host type.

   If you are _building_ compiler tools for cross-compiling, you should
use the '--target=TYPE' option to select the type of system they will
produce code for.

   If you want to _use_ a cross compiler, that generates code for a
platform different from the build platform, you should specify the host
platform (i.e., that on which the generated programs will eventually be
run) with '--host=TYPE'.  In this case, you should also specify the
build platform with '--build=TYPE', because, in this case, it may not be
possible to guess the build platform (it sometimes involves compiling
and running simple test programs, and this can't be done if the compiler
is a cross compiler).


File: autoconf.info,  Node: Sharing Defaults,  Next: Environment Variables,  Prev: System Type,  Up: Running configure scripts

13.7 Sharing Defaults
=====================

If you want to set default values for 'configure' scripts to share, you
can create a site shell script called 'config.site' that gives default
values for variables like 'CC', 'cache_file', and 'prefix'.  'configure'
looks for 'PREFIX/share/config.site' if it exists, then
'PREFIX/etc/config.site' if it exists.  Or, you can set the
'CONFIG_SITE' environment variable to the location of the site script.
A warning: not all 'configure' scripts look for a site script.


File: autoconf.info,  Node: Environment Variables,  Next: configure Invocation,  Prev: Sharing Defaults,  Up: Running configure scripts

13.8 Environment Variables
==========================

Variables not defined in a site shell script can be set in the
environment passed to configure.  However, some packages may run
configure again during the build, and the customized values of these
variables may be lost.  In order to avoid this problem, you should set
them in the 'configure' command line, using 'VAR=value'.  For example:

     ./configure CC=/usr/local2/bin/gcc

will cause the specified gcc to be used as the C compiler (unless it is
overridden in the site shell script).


File: autoconf.info,  Node: configure Invocation,  Prev: Environment Variables,  Up: Running configure scripts

13.9 'configure' Invocation
===========================

'configure' recognizes the following options to control how it operates.

'--help'
'-h'
     Print a summary of the options to 'configure', and exit.

'--version'
'-V'
     Print the version of Autoconf used to generate the 'configure'
     script, and exit.

'--cache-file=FILE'
     Enable the cache: use and save the results of the tests in FILE,
     traditionally 'config.cache'.  FILE defaults to '/dev/null' to
     disable caching.

'--config-cache'
'-C'
     Alias for '--cache-file=config.cache'.

'--quiet'
'--silent'
'-q'
     Do not print messages saying which checks are being made.  To
     suppress all normal output, redirect it to '/dev/null' (any error
     messages will still be shown).

'--srcdir=DIR'
     Look for the package's source code in directory DIR.  Usually
     'configure' can determine that directory automatically.

'configure' also accepts some other, not widely useful, options.  Run
'configure --help' for more details.


File: autoconf.info,  Node: config.status Invocation,  Next: Obsolete Constructs,  Prev: Running configure scripts,  Up: Top

14 Recreating a Configuration
*****************************

The 'configure' script creates a file named 'config.status', which
actually configures, "instantiates", the template files.  It also
records the configuration options that were specified when the package
was last configured in case reconfiguring is needed.

   Synopsis:
     ./config.status OPTION... [FILE...]

   It configures the FILES, if none are specified, all the templates are
instantiated.  The files must be specified without their dependencies,
as in

     ./config.status foobar

not

     ./config.status foobar:foo.in:bar.in

   The supported OPTIONs are:

'--help'
'-h'
     Print a summary of the command line options, the list of the
     template files and exit.

'--version'
'-V'
     Print the version number of Autoconf and exit.

'--debug'
'-d'
     Don't remove the temporary files.

'--file=FILE[:TEMPLATE]'
     Require that FILE be instantiated as if
     'AC_CONFIG_FILES(FILE:TEMPLATE)' was used.  Both FILE and TEMPLATE
     may be '-' in which case the standard output and/or standard input,
     respectively, is used.  If a TEMPLATE filename is relative, it is
     first looked for in the build tree, and then in the source tree.
     *Note Configuration Actions::, for more details.

     This option and the following ones provide one way for separately
     distributed packages to share the values computed by 'configure'.
     Doing so can be useful if some of the packages need a superset of
     the features that one of them, perhaps a common library, does.
     These options allow a 'config.status' file to create files other
     than the ones that its 'configure.ac' specifies, so it can be used
     for a different package.

'--header=FILE[:TEMPLATE]'
     Same as '--file' above, but with 'AC_CONFIG_HEADERS'.

'--recheck'
     Ask 'config.status' to update itself and exit (no instantiation).
     This option is useful if you change 'configure', so that the
     results of some tests might be different from the previous run.
     The '--recheck' option re-runs 'configure' with the same arguments
     you used before, plus the '--no-create' option, which prevents
     'configure' from running 'config.status' and creating 'Makefile'
     and other files, and the '--no-recursion' option, which prevents
     'configure' from running other 'configure' scripts in
     subdirectories.  (This is so other 'Makefile' rules can run
     'config.status' when it changes; *note Automatic Remaking::, for an
     example).

   'config.status' checks several optional environment variables that
can alter its behavior:

 -- Variable: CONFIG_SHELL
     The shell with which to run 'configure' for the '--recheck' option.
     It must be Bourne-compatible.  The default is '/bin/sh'.

 -- Variable: CONFIG_STATUS
     The file name to use for the shell script that records the
     configuration.  The default is './config.status'.  This variable is
     useful when one package uses parts of another and the 'configure'
     scripts shouldn't be merged because they are maintained separately.

   You can use './config.status' in your Makefiles.  For example, in the
dependencies given above (*note Automatic Remaking::), 'config.status'
is run twice when 'configure.ac' has changed.  If that bothers you, you
can make each run only regenerate the files for that rule:
     config.h: stamp-h
     stamp-h: config.h.in config.status
             ./config.status config.h
             echo > stamp-h

     Makefile: Makefile.in config.status
             ./config.status Makefile

   The calling convention of 'config.status' has changed, see *note
Obsolete config.status Use::, for details.


File: autoconf.info,  Node: Obsolete Constructs,  Next: Questions,  Prev: config.status Invocation,  Up: Top

15 Obsolete Constructs
**********************

Autoconf changes, and throughout the years some constructs are
obsoleted.  Most of the changes involve the macros, but the tools
themselves, or even some concepts, are now considered obsolete.

   You may completely skip this chapter if you are new to Autoconf, its
intention is mainly to help maintainers updating their packages by
understanding how to move to more modern constructs.

* Menu:

* Obsolete config.status Use::  Different calling convention
* acconfig.h::                  Additional entries in 'config.h.in'
* autoupdate Invocation::       Automatic update of 'configure.ac'
* Obsolete Macros::             Backward compatibility macros
* Autoconf 1::                  Tips for upgrading your files
* Autoconf 2.13::               Some fresher tips


File: autoconf.info,  Node: Obsolete config.status Use,  Next: acconfig.h,  Prev: Obsolete Constructs,  Up: Obsolete Constructs

15.1 Obsolete 'config.status' Invocation
========================================

'config.status' now supports arguments to specify the files to
instantiate, see *note config.status Invocation::, for more details.
Before, environment variables had to be used.

 -- Variable: CONFIG_COMMANDS
     The tags of the commands to execute.  The default is the arguments
     given to 'AC_OUTPUT' and 'AC_CONFIG_COMMANDS' in 'configure.ac'.

 -- Variable: CONFIG_FILES
     The files in which to perform '@VARIABLE@' substitutions.  The
     default is the arguments given to 'AC_OUTPUT' and 'AC_CONFIG_FILES'
     in 'configure.ac'.

 -- Variable: CONFIG_HEADERS
     The files in which to substitute C '#define' statements.  The
     default is the arguments given to 'AC_CONFIG_HEADERS'; if that
     macro was not called, 'config.status' ignores this variable.

 -- Variable: CONFIG_LINKS
     The symbolic links to establish.  The default is the arguments
     given to 'AC_CONFIG_LINKS'; if that macro was not called,
     'config.status' ignores this variable.

   In *note config.status Invocation::, using this old interface, the
example would be:

     config.h: stamp-h
     stamp-h: config.h.in config.status
             CONFIG_COMMANDS= CONFIG_LINKS= CONFIG_FILES= \
               CONFIG_HEADERS=config.h ./config.status
             echo > stamp-h

     Makefile: Makefile.in config.status
             CONFIG_COMMANDS= CONFIG_LINKS= CONFIG_HEADERS= \
               CONFIG_FILES=Makefile ./config.status

(If 'configure.ac' does not call 'AC_CONFIG_HEADERS', there is no need
to set 'CONFIG_HEADERS' in the 'make' rules, equally for
'CONFIG_COMMANDS' etc.)


File: autoconf.info,  Node: acconfig.h,  Next: autoupdate Invocation,  Prev: Obsolete config.status Use,  Up: Obsolete Constructs

15.2 'acconfig.h'
=================

In order to produce 'config.h.in', 'autoheader' needs to build or to
find templates for each symbol.  Modern releases of Autoconf use
'AH_VERBATIM' and 'AH_TEMPLATE' (*note Autoheader Macros::), but in
older releases a file, 'acconfig.h', contained the list of needed
templates.  'autoheader' copies comments and '#define' and '#undef'
statements from 'acconfig.h' in the current directory, if present.  This
file used to be mandatory if you 'AC_DEFINE' any additional symbols.

   Modern releases of Autoconf also provide 'AH_TOP' and 'AH_BOTTOM' if
you need to prepend/append some information to 'config.h.in'.  Ancient
versions of Autoconf had a similar feature: if './acconfig.h' contains
the string '@TOP@', 'autoheader' copies the lines before the line
containing '@TOP@' into the top of the file that it generates.
Similarly, if './acconfig.h' contains the string '@BOTTOM@',
'autoheader' copies the lines after that line to the end of the file it
generates.  Either or both of those strings may be omitted.  An even
older alternate way to produce the same effect in jurasik versions of
Autoconf is to create the files 'FILE.top' (typically 'config.h.top')
and/or 'FILE.bot' in the current directory.  If they exist, 'autoheader'
copies them to the beginning and end, respectively, of its output.

   In former versions of Autoconf, the files used in preparing a
software package for distribution were:
     configure.ac --.   .------> autoconf* -----> configure
                    +---+
     [aclocal.m4] --+   `---.
     [acsite.m4] ---'       |
                            +--> [autoheader*] -> [config.h.in]
     [acconfig.h] ----.     |
                      +-----'
     [config.h.top] --+
     [config.h.bot] --'

   Use only the 'AH_' macros, 'configure.ac' should be self-contained,
and should not depend upon 'acconfig.h' etc.


File: autoconf.info,  Node: autoupdate Invocation,  Next: Obsolete Macros,  Prev: acconfig.h,  Up: Obsolete Constructs

15.3 Using 'autoupdate' to Modernize 'configure.ac'
===================================================

The 'autoupdate' program updates a 'configure.ac' file that calls
Autoconf macros by their old names to use the current macro names.  In
version 2 of Autoconf, most of the macros were renamed to use a more
uniform and descriptive naming scheme.  *Note Macro Names::, for a
description of the new scheme.  Although the old names still work (*note
Obsolete Macros::, for a list of the old macros and the corresponding
new names), you can make your 'configure.ac' files more readable and
make it easier to use the current Autoconf documentation if you update
them to use the new macro names.

   If given no arguments, 'autoupdate' updates 'configure.ac', backing
up the original version with the suffix '~' (or the value of the
environment variable 'SIMPLE_BACKUP_SUFFIX', if that is set).  If you
give 'autoupdate' an argument, it reads that file instead of
'configure.ac' and writes the updated file to the standard output.

'autoupdate' accepts the following options:

'--help'
'-h'
     Print a summary of the command line options and exit.

'--version'
'-V'
     Print the version number of Autoconf and exit.

'--verbose'
'-v'
     Report processing steps.

'--debug'
'-d'
     Don't remove the temporary files.

'--autoconf-dir=DIR'
'-A DIR'
     Override the location where the installed Autoconf data files are
     looked for.  You can also set the 'AC_MACRODIR' environment
     variable to a directory; this option overrides the environment
     variable.

     This option is rarely needed and dangerous; it is only used when
     one plays with different versions of Autoconf simultaneously.

'--localdir=DIR'
'-l DIR'
     Look for the package file 'aclocal.m4' in directory DIR instead of
     in the current directory.


File: autoconf.info,  Node: Obsolete Macros,  Next: Autoconf 1,  Prev: autoupdate Invocation,  Up: Obsolete Constructs

15.4 Obsolete Macros
====================

Several macros are obsoleted in Autoconf, for various reasons (typically
they failed to quote properly, couldn't be extended for more recent
issues etc.).  They are still supported, but deprecated: their use
should be avoided.

   During the jump from Autoconf version 1 to version 2, most of the
macros were renamed to use a more uniform and descriptive naming scheme,
but their signature did not change.  *Note Macro Names::, for a
description of the new naming scheme.  Below, there is just the mapping
from old names to new names for these macros, the reader is invited to
refer to the definition of the new macro for the signature and the
description.

 -- Macro: AC_ALLOCA
     'AC_FUNC_ALLOCA'

 -- Macro: AC_ARG_ARRAY
     removed because of limited usefulness

 -- Macro: AC_C_CROSS
     This macro is obsolete; it does nothing.

 -- Macro: AC_CANONICAL_SYSTEM
     Determine the system type and set output variables to the names of
     the canonical system types.  *Note Canonicalizing::, for details
     about the variables this macro sets.

     The user is encouraged to use either 'AC_CANONICAL_BUILD', or
     'AC_CANONICAL_HOST', or 'AC_CANONICAL_TARGET', depending on the
     needs.  Using 'AC_CANONICAL_TARGET' is enough to run the two other
     macros.

 -- Macro: AC_CHAR_UNSIGNED
     'AC_C_CHAR_UNSIGNED'

 -- Macro: AC_CHECK_TYPE (TYPE, DEFAULT)
     Autoconf, up to 2.13, used to provide this version of
     'AC_CHECK_TYPE', deprecated because of its flaws.  Firstly,
     although it is a member of the 'CHECK' clan, singular sub-family,
     it does more than just checking.  Second, missing types are not
     'typedef''d, they are '#define''d, which can lead to incompatible
     code in the case of pointer types.

     This use of 'AC_CHECK_TYPE' is obsolete and discouraged, see *note
     Generic Types::, for the description of the current macro.

     If the type TYPE is not defined, define it to be the C (or C++)
     builtin type DEFAULT; e.g., 'short' or 'unsigned'.

     This macro is equivalent to:

          AC_CHECK_TYPE([TYPE],
                        [AC_DEFINE([TYPE], [DEFAULT],
                                   [Define to `DEFAULT' if <sys/types.h>
                                    does not define.])])

     In order to keep backward compatibility, the two versions of
     'AC_CHECK_TYPE' are implemented, selected by a simple heuristics:

       1. If there are three or four arguments, the modern version is
          used.

       2. If the second argument appears to be a C or C++ type, then the
          obsolete version is used.  This happens if the argument is a C
          or C++ _builtin_ type or a C identifier ending in '_t',
          optionally followed by one of '[(* ' and then by a string of
          zero or more characters taken from the set '[]()* _a-zA-Z0-9'.

       3. If the second argument is spelled with the alphabet of valid C
          and C++ types, the user is warned and the modern version is
          used.

       4. Otherwise, the modern version is used.

     You are encouraged either to use a valid builtin type, or to use
     the equivalent modern code (see above), or better yet, to use
     'AC_CHECK_TYPES' together with

          #if !HAVE_LOFF_T
          typedef loff_t off_t;
          #endif

 -- Macro: AC_CHECKING (FEATURE-DESCRIPTION)
     Same as 'AC_MSG_NOTICE([checking FEATURE-DESCRIPTION...]'.

 -- Macro: AC_COMPILE_CHECK (ECHO-TEXT, INCLUDES, FUNCTION-BODY,
          ACTION-IF-FOUND, [ACTION-IF-NOT-FOUND])
     This is an obsolete version of 'AC_TRY_LINK' (*note Examining
     Libraries::), with the addition that it prints 'checking for
     ECHO-TEXT' to the standard output first, if ECHO-TEXT is non-empty.
     Use 'AC_MSG_CHECKING' and 'AC_MSG_RESULT' instead to print messages
     (*note Printing Messages::).

 -- Macro: AC_CONST
     'AC_C_CONST'

 -- Macro: AC_CROSS_CHECK
     Same as 'AC_C_CROSS', which is obsolete too, and does nothing
     ':-)'.

 -- Macro: AC_CYGWIN
     Check for the Cygwin environment in which case the shell variable
     'CYGWIN' is set to 'yes'.  Don't use this macro, the dignified
     means to check the nature of the host is using 'AC_CANONICAL_HOST'.
     As a matter of fact this macro is defined as:

          AC_REQUIRE([AC_CANONICAL_HOST])[]dnl
          case $host_os in
            *cygwin* ) CYGWIN=yes;;
                   * ) CYGWIN=no;;
          esac

     Beware that the variable 'CYGWIN' has a very special meaning when
     running CygWin32, and should not be changed.  That's yet another
     reason not to use this macro.

 -- Macro: AC_DECL_YYTEXT
     Does nothing, now integrated in 'AC_PROG_LEX'.

 -- Macro: AC_DIR_HEADER
     Like calling 'AC_FUNC_CLOSEDIR_VOID' and'AC_HEADER_DIRENT', but
     defines a different set of C preprocessor macros to indicate which
     header file is found:

     Header         Old Symbol   New Symbol
     'dirent.h'     'DIRENT'     'HAVE_DIRENT_H'
     'sys/ndir.h'   'SYSNDIR'    'HAVE_SYS_NDIR_H'
     'sys/dir.h'    'SYSDIR'     'HAVE_SYS_DIR_H'
     'ndir.h'       'NDIR'       'HAVE_NDIR_H'

 -- Macro: AC_DYNIX_SEQ
     If on Dynix/PTX (Sequent UNIX), add '-lseq' to output variable
     'LIBS'.  This macro used to be defined as

          AC_CHECK_LIB(seq, getmntent, LIBS="-lseq $LIBS")

     now it is just 'AC_FUNC_GETMNTENT'.

 -- Macro: AC_EXEEXT
     Defined the output variable 'EXEEXT' based on the output of the
     compiler, which is now done automatically.  Typically set to empty
     string if Unix and '.exe' if Win32 or OS/2.

 -- Macro: AC_EMXOS2
     Similar to 'AC_CYGWIN' but checks for the EMX environment on OS/2
     and sets 'EMXOS2'.

 -- Macro: AC_ERROR
     'AC_MSG_ERROR'

 -- Macro: AC_FIND_X
     'AC_PATH_X'

 -- Macro: AC_FIND_XTRA
     'AC_PATH_XTRA'

 -- Macro: AC_FUNC_CHECK
     'AC_CHECK_FUNC'

 -- Macro: AC_FUNC_WAIT3
     If 'wait3' is found and fills in the contents of its third argument
     (a 'struct rusage *'), which HP-UX does not do, define
     'HAVE_WAIT3'.

     These days portable programs should use 'waitpid', not 'wait3', as
     'wait3' is being removed from the Open Group standards, and will
     not appear in the next revision of POSIX.

 -- Macro: AC_GCC_TRADITIONAL
     'AC_PROG_GCC_TRADITIONAL'

 -- Macro: AC_GETGROUPS_T
     'AC_TYPE_GETGROUPS'

 -- Macro: AC_GETLOADAVG
     'AC_FUNC_GETLOADAVG'

 -- Macro: AC_HAVE_FUNCS
     'AC_CHECK_FUNCS'

 -- Macro: AC_HAVE_HEADERS
     'AC_CHECK_HEADERS'

 -- Macro: AC_HAVE_LIBRARY (LIBRARY, [ACTION-IF-FOUND],
          [ACTION-IF-NOT-FOUND], [OTHER-LIBRARIES])
     This macro is equivalent to calling 'AC_CHECK_LIB' with a FUNCTION
     argument of 'main'.  In addition, LIBRARY can be written as any of
     'foo', '-lfoo', or 'libfoo.a'.  In all of those cases, the compiler
     is passed '-lfoo'.  However, LIBRARY cannot be a shell variable; it
     must be a literal name.

 -- Macro: AC_HAVE_POUNDBANG
     'AC_SYS_INTERPRETER' (different calling convention)

 -- Macro: AC_HEADER_CHECK
     'AC_CHECK_HEADER'

 -- Macro: AC_HEADER_EGREP
     'AC_EGREP_HEADER'

 -- Macro: AC_INIT (UNIQUE-FILE-IN-SOURCE-DIR)
     Formerly 'AC_INIT' used to have a single argument, and was
     equivalent to:

          AC_INIT
          AC_CONFIG_SRCDIR(UNIQUE-FILE-IN-SOURCE-DIR)

 -- Macro: AC_INLINE
     'AC_C_INLINE'

 -- Macro: AC_INT_16_BITS
     If the C type 'int' is 16 bits wide, define 'INT_16_BITS'.  Use
     'AC_CHECK_SIZEOF(int)' instead.

 -- Macro: AC_IRIX_SUN
     If on IRIX (Silicon Graphics UNIX), add '-lsun' to output 'LIBS'.
     If you were using it to get 'getmntent', use 'AC_FUNC_GETMNTENT'
     instead.  If you used it for the NIS versions of the password and
     group functions, use 'AC_CHECK_LIB(sun, getpwnam)'.  Up to Autoconf
     2.13, it used to be

          AC_CHECK_LIB(sun, getmntent, LIBS="-lsun $LIBS")

     now it is defined as

          AC_FUNC_GETMNTENT
          AC_CHECK_LIB(sun, getpwnam)

 -- Macro: AC_LANG_C
     Same as 'AC_LANG(C)'.

 -- Macro: AC_LANG_CPLUSPLUS
     Same as 'AC_LANG(C++)'.

 -- Macro: AC_LANG_FORTRAN77
     Same as 'AC_LANG(Fortran 77)'.

 -- Macro: AC_LANG_RESTORE
     Select the LANGUAGE that is saved on the top of the stack, as set
     by 'AC_LANG_SAVE', remove it from the stack, and call
     'AC_LANG(LANGUAGE)'.

 -- Macro: AC_LANG_SAVE
     Remember the current language (as set by 'AC_LANG') on a stack.
     The current language does not change.  'AC_LANG_PUSH' is preferred.

 -- Macro: AC_LINK_FILES (SOURCE..., DEST...)
     This is an obsolete version of 'AC_CONFIG_LINKS'.  An updated
     version of:

          AC_LINK_FILES(config/$machine.h config/$obj_format.h,
                        host.h            object.h)

     is:

          AC_CONFIG_LINKS(host.h:config/$machine.h
                          object.h:config/$obj_format.h)

 -- Macro: AC_LN_S
     'AC_PROG_LN_S'

 -- Macro: AC_LONG_64_BITS
     Define 'LONG_64_BITS' if the C type 'long int' is 64 bits wide.
     Use the generic macro 'AC_CHECK_SIZEOF([long int])' instead.

 -- Macro: AC_LONG_DOUBLE
     'AC_C_LONG_DOUBLE'

 -- Macro: AC_LONG_FILE_NAMES
     'AC_SYS_LONG_FILE_NAMES'

 -- Macro: AC_MAJOR_HEADER
     'AC_HEADER_MAJOR'

 -- Macro: AC_MEMORY_H
     Used to define 'NEED_MEMORY_H' if the 'mem' functions were defined
     in 'memory.h'.  Today it is equivalent to
     'AC_CHECK_HEADERS(memory.h)'.  Adjust your code to depend upon
     'HAVE_MEMORY_H', not 'NEED_MEMORY_H', see *Note Standard Symbols::.

 -- Macro: AC_MINGW32
     Similar to 'AC_CYGWIN' but checks for the MingW32 compiler
     environment and sets 'MINGW32'.

 -- Macro: AC_MINUS_C_MINUS_O
     'AC_PROG_CC_C_O'

 -- Macro: AC_MMAP
     'AC_FUNC_MMAP'

 -- Macro: AC_MODE_T
     'AC_TYPE_MODE_T'

 -- Macro: AC_OBJEXT
     Defined the output variable 'OBJEXT' based on the output of the
     compiler, after .c files have been excluded.  Typically set to 'o'
     if Unix, 'obj' if Win32.  Now the compiler checking macros handle
     this automatically.

 -- Macro: AC_OBSOLETE (THIS-MACRO-NAME, [SUGGESTION])
     Make 'm4' print a message to the standard error output warning that
     THIS-MACRO-NAME is obsolete, and giving the file and line number
     where it was called.  THIS-MACRO-NAME should be the name of the
     macro that is calling 'AC_OBSOLETE'.  If SUGGESTION is given, it is
     printed at the end of the warning message; for example, it can be a
     suggestion for what to use instead of THIS-MACRO-NAME.

     For instance

          AC_OBSOLETE([$0], [; use AC_CHECK_HEADERS(unistd.h) instead])dnl

     You are encouraged to use 'AU_DEFUN' instead, since it gives better
     services to the user.

 -- Macro: AC_OFF_T
     'AC_TYPE_OFF_T'

 -- Macro: AC_OUTPUT ([FILE]..., [EXTRA-CMDS], [INIT-CMDS], [SAVE-DEFS])
     The use of 'AC_OUTPUT' with argument is deprecated, this obsoleted
     interface is equivalent to:

          AC_CONFIG_FILES(FILE...)
          AC_CONFIG_COMMANDS([default],
                             EXTRA-CMDS, INIT-CMDS)
          AC_SETUP_DEFS(SAVE-DEFS)
          AC_OUTPUT

     If you specify SAVE-DEFS, autoconf will save the '#define's in a
     different form, for use in the files specified in
     'AC_CONFIG_HEADERS'.  In this case, autoconf substitutes the
     C-style '#define's where it finds '@DEFS@'.  This runs faster, and
     is simpler to maintain than building a file of '#undef's, since
     autoconf will automatically generate a '#define' for each
     'AC_DEFINE' that you execute in the 'configure' script.  The value
     for SAVE-DEFS should be either 'cat', or 'sort'; this value is used
     to filter the list of '#define's before editing.  Sorted lists are
     easier to read, but you may wish to see the definitions in the
     order that they were processed.

 -- Macro: AC_OUTPUT_COMMANDS (EXTRA-CMDS, [INIT-CMDS])
     Specify additional shell commands to run at the end of
     'config.status', and shell commands to initialize any variables
     from 'configure'.  This macro may be called multiple times.  It is
     obsolete, replaced by 'AC_CONFIG_COMMANDS'.

     Here is an unrealistic example:

          fubar=27
          AC_OUTPUT_COMMANDS([echo this is extra $fubar, and so on.],
                             fubar=$fubar)
          AC_OUTPUT_COMMANDS([echo this is another, extra, bit],
                             [echo init bit])

     Aside from the fact that 'AC_CONFIG_COMMANDS' requires an
     additional key, an important difference is that
     'AC_OUTPUT_COMMANDS' is quoting its arguments twice, while
     'AC_CONFIG_COMMANDS'.  This means that 'AC_CONFIG_COMMANDS' can
     safely be given macro calls as arguments:

          AC_CONFIG_COMMANDS(foo, [my_FOO()])

     conversely, where one level of quoting was enough for literal
     strings with 'AC_OUTPUT_COMMANDS', you need two with
     'AC_CONFIG_COMMANDS'.  The following lines are equivalent:

          AC_OUTPUT_COMMANDS([echo "Square brackets: []"])
          AC_CONFIG_COMMANDS(default, [[echo "Square brackets: []"]])

 -- Macro: AC_PID_T
     'AC_TYPE_PID_T'

 -- Macro: AC_PREFIX
     'AC_PREFIX_PROGRAM'

 -- Macro: AC_PROGRAMS_CHECK
     'AC_CHECK_PROGS'

 -- Macro: AC_PROGRAMS_PATH
     'AC_PATH_PROGS'

 -- Macro: AC_PROGRAM_CHECK
     'AC_CHECK_PROG'

 -- Macro: AC_PROGRAM_EGREP
     'AC_EGREP_CPP'

 -- Macro: AC_PROGRAM_PATH
     'AC_PATH_PROG'

 -- Macro: AC_REMOTE_TAPE
     removed because of limited usefulness

 -- Macro: AC_RESTARTABLE_SYSCALLS
     'AC_SYS_RESTARTABLE_SYSCALLS'

 -- Macro: AC_RETSIGTYPE
     'AC_TYPE_SIGNAL'

 -- Macro: AC_RSH
     Removed because of limited usefulness.

 -- Macro: AC_SCO_INTL
     If on SCO UNIX, add '-lintl' to output variable 'LIBS'.  This macro
     used to

          AC_CHECK_LIB(intl, strftime, LIBS="-lintl $LIBS")

     now it just calls 'AC_FUNC_STRFTIME' instead.

 -- Macro: AC_SETVBUF_REVERSED
     'AC_FUNC_SETVBUF_REVERSED'

 -- Macro: AC_SET_MAKE
     'AC_PROG_MAKE_SET'

 -- Macro: AC_SIZEOF_TYPE
     'AC_CHECK_SIZEOF'

 -- Macro: AC_SIZE_T
     'AC_TYPE_SIZE_T'

 -- Macro: AC_STAT_MACROS_BROKEN
     'AC_HEADER_STAT'

 -- Macro: AC_STDC_HEADERS
     'AC_HEADER_STDC'

 -- Macro: AC_STRCOLL
     'AC_FUNC_STRCOLL'

 -- Macro: AC_ST_BLKSIZE
     'AC_STRUCT_ST_BLKSIZE'

 -- Macro: AC_ST_BLOCKS
     'AC_STRUCT_ST_BLOCKS'

 -- Macro: AC_ST_RDEV
     'AC_STRUCT_ST_RDEV'

 -- Macro: AC_SYS_RESTARTABLE_SYSCALLS
     If the system automatically restarts a system call that is
     interrupted by a signal, define 'HAVE_RESTARTABLE_SYSCALLS'.  This
     macro does not check if system calls are restarted in general-it
     tests whether a signal handler installed with 'signal' (but not
     'sigaction') causes system calls to be restarted.  It does not test
     if system calls can be restarted when interrupted by signals that
     have no handler.

     These days portable programs should use 'sigaction' with
     'SA_RESTART' if they want restartable system calls.  They should
     not rely on 'HAVE_RESTARTABLE_SYSCALLS', since nowadays whether a
     system call is restartable is a dynamic issue, not a
     configuration-time issue.

 -- Macro: AC_SYS_SIGLIST_DECLARED
     'AC_DECL_SYS_SIGLIST'

 -- Macro: AC_TEST_CPP
     'AC_TRY_CPP'

 -- Macro: AC_TEST_PROGRAM
     'AC_TRY_RUN'

 -- Macro: AC_TIMEZONE
     'AC_STRUCT_TIMEZONE'

 -- Macro: AC_TIME_WITH_SYS_TIME
     'AC_HEADER_TIME'

 -- Macro: AC_UID_T
     'AC_TYPE_UID_T'

 -- Macro: AC_UNISTD_H
     Same as 'AC_CHECK_HEADERS(unistd.h)'.

 -- Macro: AC_USG
     Define 'USG' if the BSD string functions are defined in
     'strings.h'.  You should no longer depend upon 'USG', but on
     'HAVE_STRING_H', see *Note Standard Symbols::.

 -- Macro: AC_UTIME_NULL
     'AC_FUNC_UTIME_NULL'

 -- Macro: AC_VALIDATE_CACHED_SYSTEM_TUPLE ([CMD])
     If the cache file is inconsistent with the current host, target and
     build system types, it used to execute CMD or print a default error
     message.

     This is now handled by default.

 -- Macro: AC_VERBOSE (RESULT-DESCRIPTION)
     'AC_MSG_RESULT'.

 -- Macro: AC_VFORK
     'AC_FUNC_VFORK'

 -- Macro: AC_VPRINTF
     'AC_FUNC_VPRINTF'

 -- Macro: AC_WAIT3
     'AC_FUNC_WAIT3'

 -- Macro: AC_WARN
     'AC_MSG_WARN'

 -- Macro: AC_WORDS_BIGENDIAN
     'AC_C_BIGENDIAN'

 -- Macro: AC_XENIX_DIR
     This macro used to add '-lx' to output variable 'LIBS' if on Xenix.
     Also, if 'dirent.h' is being checked for, added '-ldir' to 'LIBS'.
     Now it is merely an alias of 'AC_HEADER_DIRENT' instead, plus some
     code to detect whether running XENIX on which you should not
     depend:

          AC_MSG_CHECKING([for Xenix])
          AC_EGREP_CPP(yes,
          [#if defined M_XENIX && !defined M_UNIX
            yes
          #endif],
                       [AC_MSG_RESULT([yes]); XENIX=yes],
                       [AC_MSG_RESULT([no]); XENIX=])

 -- Macro: AC_YYTEXT_POINTER
     'AC_DECL_YYTEXT'


File: autoconf.info,  Node: Autoconf 1,  Next: Autoconf 2.13,  Prev: Obsolete Macros,  Up: Obsolete Constructs

15.5 Upgrading From Version 1
=============================

Autoconf version 2 is mostly backward compatible with version 1.
However, it introduces better ways to do some things, and doesn't
support some of the ugly things in version 1.  So, depending on how
sophisticated your 'configure.ac' files are, you might have to do some
manual work in order to upgrade to version 2.  This chapter points out
some problems to watch for when upgrading.  Also, perhaps your
'configure' scripts could benefit from some of the new features in
version 2; the changes are summarized in the file 'NEWS' in the Autoconf
distribution.

* Menu:

* Changed File Names::          Files you might rename
* Changed Makefiles::           New things to put in 'Makefile.in'
* Changed Macros::              Macro calls you might replace
* Changed Results::             Changes in how to check test results
* Changed Macro Writing::       Better ways to write your own macros


File: autoconf.info,  Node: Changed File Names,  Next: Changed Makefiles,  Prev: Autoconf 1,  Up: Autoconf 1

15.5.1 Changed File Names
-------------------------

If you have an 'aclocal.m4' installed with Autoconf (as opposed to in a
particular package's source directory), you must rename it to
'acsite.m4'.  *Note autoconf Invocation::.

   If you distribute 'install.sh' with your package, rename it to
'install-sh' so 'make' builtin rules won't inadvertently create a file
called 'install' from it.  'AC_PROG_INSTALL' looks for the script under
both names, but it is best to use the new name.

   If you were using 'config.h.top', 'config.h.bot', or 'acconfig.h',
you still can, but you will have less clutter if you use the 'AH_'
macros.  *Note Autoheader Macros::.


File: autoconf.info,  Node: Changed Makefiles,  Next: Changed Macros,  Prev: Changed File Names,  Up: Autoconf 1

15.5.2 Changed Makefiles
------------------------

Add '@CFLAGS@', '@CPPFLAGS@', and '@LDFLAGS@' in your 'Makefile.in'
files, so they can take advantage of the values of those variables in
the environment when 'configure' is run.  Doing this isn't necessary,
but it's a convenience for users.

   Also add '@configure_input@' in a comment to each input file for
'AC_OUTPUT', so that the output files will contain a comment saying they
were produced by 'configure'.  Automatically selecting the right comment
syntax for all the kinds of files that people call 'AC_OUTPUT' on became
too much work.

   Add 'config.log' and 'config.cache' to the list of files you remove
in 'distclean' targets.

   If you have the following in 'Makefile.in':

     prefix = /usr/local
     exec_prefix = $(prefix)

you must change it to:

     prefix = @prefix@
     exec_prefix = @exec_prefix@

The old behavior of replacing those variables without '@' characters
around them has been removed.


File: autoconf.info,  Node: Changed Macros,  Next: Changed Results,  Prev: Changed Makefiles,  Up: Autoconf 1

15.5.3 Changed Macros
---------------------

Many of the macros were renamed in Autoconf version 2.  You can still
use the old names, but the new ones are clearer, and it's easier to find
the documentation for them.  *Note Obsolete Macros::, for a table
showing the new names for the old macros.  Use the 'autoupdate' program
to convert your 'configure.ac' to using the new macro names.  *Note
autoupdate Invocation::.

   Some macros have been superseded by similar ones that do the job
better, but are not call-compatible.  If you get warnings about calling
obsolete macros while running 'autoconf', you may safely ignore them,
but your 'configure' script will generally work better if you follow the
advice it prints about what to replace the obsolete macros with.  In
particular, the mechanism for reporting the results of tests has
changed.  If you were using 'echo' or 'AC_VERBOSE' (perhaps via
'AC_COMPILE_CHECK'), your 'configure' script's output will look better
if you switch to 'AC_MSG_CHECKING' and 'AC_MSG_RESULT'.  *Note Printing
Messages::.  Those macros work best in conjunction with cache variables.
*Note Caching Results::.


File: autoconf.info,  Node: Changed Results,  Next: Changed Macro Writing,  Prev: Changed Macros,  Up: Autoconf 1

15.5.4 Changed Results
----------------------

If you were checking the results of previous tests by examining the
shell variable 'DEFS', you need to switch to checking the values of the
cache variables for those tests.  'DEFS' no longer exists while
'configure' is running; it is only created when generating output files.
This difference from version 1 is because properly quoting the contents
of that variable turned out to be too cumbersome and inefficient to do
every time 'AC_DEFINE' is called.  *Note Cache Variable Names::.

   For example, here is a 'configure.ac' fragment written for Autoconf
version 1:

     AC_HAVE_FUNCS(syslog)
     case "$DEFS" in
     *-DHAVE_SYSLOG*) ;;
     *) # syslog is not in the default libraries.  See if it's in some other.
       saved_LIBS="$LIBS"
       for lib in bsd socket inet; do
         AC_CHECKING(for syslog in -l$lib)
         LIBS="$saved_LIBS -l$lib"
         AC_HAVE_FUNCS(syslog)
         case "$DEFS" in
         *-DHAVE_SYSLOG*) break ;;
         *) ;;
         esac
         LIBS="$saved_LIBS"
       done ;;
     esac

   Here is a way to write it for version 2:

     AC_CHECK_FUNCS(syslog)
     if test $ac_cv_func_syslog = no; then
       # syslog is not in the default libraries.  See if it's in some other.
       for lib in bsd socket inet; do
         AC_CHECK_LIB($lib, syslog, [AC_DEFINE(HAVE_SYSLOG)
           LIBS="$LIBS -l$lib"; break])
       done
     fi

   If you were working around bugs in 'AC_DEFINE_UNQUOTED' by adding
backslashes before quotes, you need to remove them.  It now works
predictably, and does not treat quotes (except back quotes) specially.
*Note Setting Output Variables::.

   All of the boolean shell variables set by Autoconf macros now use
'yes' for the true value.  Most of them use 'no' for false, though for
backward compatibility some use the empty string instead.  If you were
relying on a shell variable being set to something like 1 or 't' for
true, you need to change your tests.


File: autoconf.info,  Node: Changed Macro Writing,  Prev: Changed Results,  Up: Autoconf 1

15.5.5 Changed Macro Writing
----------------------------

When defining your own macros, you should now use 'AC_DEFUN' instead of
'define'.  'AC_DEFUN' automatically calls 'AC_PROVIDE' and ensures that
macros called via 'AC_REQUIRE' do not interrupt other macros, to prevent
nested 'checking...' messages on the screen.  There's no actual harm in
continuing to use the older way, but it's less convenient and
attractive.  *Note Macro Definitions::.

   You probably looked at the macros that came with Autoconf as a guide
for how to do things.  It would be a good idea to take a look at the new
versions of them, as the style is somewhat improved and they take
advantage of some new features.

   If you were doing tricky things with undocumented Autoconf internals
(macros, variables, diversions), check whether you need to change
anything to account for changes that have been made.  Perhaps you can
even use an officially supported technique in version 2 instead of
kludging.  Or perhaps not.

   To speed up your locally written feature tests, add caching to them.
See whether any of your tests are of general enough usefulness to
encapsulate into macros that you can share.


File: autoconf.info,  Node: Autoconf 2.13,  Prev: Autoconf 1,  Up: Obsolete Constructs

15.6 Upgrading From Version 2.13
================================

The introduction of the previous section (*note Autoconf 1::) perfectly
suits this section...

     Autoconf version 2.50 is mostly backward compatible with version
     2.13.  However, it introduces better ways to do some things, and
     doesn't support some of the ugly things in version 2.13.  So,
     depending on how sophisticated your 'configure.ac' files are, you
     might have to do some manual work in order to upgrade to version
     2.50.  This chapter points out some problems to watch for when
     upgrading.  Also, perhaps your 'configure' scripts could benefit
     from some of the new features in version 2.50; the changes are
     summarized in the file 'NEWS' in the Autoconf distribution.

* Menu:

* Changed Quotation::           Broken code which used to work
* New Macros::                  Interaction with foreign macros


File: autoconf.info,  Node: Changed Quotation,  Next: New Macros,  Prev: Autoconf 2.13,  Up: Autoconf 2.13

15.6.1 Changed Quotation
------------------------

The most important changes are invisible to you: the implementation of
most macros have completely changed.  This allowed more factorization of
the code, better error messages, a higher uniformity of the user's
interface etc.  Unfortunately, as a side effect, some construct which
used to (miraculously) work might break starting with Autoconf 2.50.
The most common culprit is bad quotation.

   For instance, in the following example, the message is not properly
quoted:

     AC_INIT
     AC_CHECK_HEADERS(foo.h,,
     AC_MSG_ERROR(cannot find foo.h, bailing out))
     AC_OUTPUT

Autoconf 2.13 simply ignores it:

     $ autoconf-2.13; ./configure --silent
     creating cache ./config.cache
     configure: error: cannot find foo.h
     $

while Autoconf 2.50 will produce a broken 'configure':

     $ autoconf-2.50; ./configure --silent
     configure: error: cannot find foo.h
     ./configure: exit: bad non-numeric arg `bailing'
     ./configure: exit: bad non-numeric arg `bailing'
     $

   The message needs to be quoted, and the 'AC_MSG_ERROR' invocation
too!

     AC_INIT
     AC_CHECK_HEADERS(foo.h,,
                      [AC_MSG_ERROR([cannot find foo.h, bailing out])])
     AC_OUTPUT

   Many many (and many more) Autoconf macros were lacking proper
quotation, including no less than...  'AC_DEFUN' itself!

     $ cat configure.in
     AC_DEFUN([AC_PROG_INSTALL],
     [# My own much better version
     ])
     AC_INIT
     AC_PROG_INSTALL
     AC_OUTPUT
     $ autoconf-2.13
     autoconf: Undefined macros:
     ***BUG in Autoconf--please report*** AC_FD_MSG
     ***BUG in Autoconf--please report*** AC_EPI
     configure.in:1:AC_DEFUN([AC_PROG_INSTALL],
     configure.in:5:AC_PROG_INSTALL
     $ autoconf-2.50
     $


File: autoconf.info,  Node: New Macros,  Prev: Changed Quotation,  Up: Autoconf 2.13

15.6.2 New Macros
-----------------

Because Autoconf has been dormant for years, Automake provided
Autoconf-like macros for a while.  Autoconf 2.50 now provides better
versions of these macros, integrated in the 'AC_' namespace, instead of
'AM_'.  But in order to ease the upgrading via 'autoupdate', bindings to
such 'AM_' macros are provided.

   Unfortunately Automake did not quote the name of these macros!
Therefore, when 'm4' find in 'aclocal.m4' something like
'AC_DEFUN(AM_TYPE_PTRDIFF_T, ...)', 'AM_TYPE_PTRDIFF_T' is expanded,
replaced with its Autoconf definition.

   Fortunately Autoconf catches pre-'AC_INIT' expansions, and will
complain, in its own words:

     $ cat configure.in
     AC_INIT
     AM_TYPE_PTRDIFF_T
     $ aclocal-1.4
     $ autoconf
     ./aclocal.m4:17: error: m4_defn: undefined macro: _m4_divert_diversion
     actypes.m4:289: AM_TYPE_PTRDIFF_T is expanded from...
     ./aclocal.m4:17: the top level
     $

   Future versions of Automake will simply no longer define most of
these macros, and will properly quote the names of the remaining macros.
But you don't have to wait for it to happen to do the right thing right
now: do not depend upon macros from Automake as it is simply not its job
to provide macros (but the one it requires by itself):

     $ cat configure.in
     AC_INIT
     AM_TYPE_PTRDIFF_T
     $ rm aclocal.m4
     $ autoupdate
     autoupdate: `configure.in' is updated
     $ cat configure.in
     AC_INIT
     AC_CHECK_TYPES([ptrdiff_t])
     $ aclocal-1.4
     $ autoconf
     $


File: autoconf.info,  Node: Questions,  Next: History,  Prev: Obsolete Constructs,  Up: Top

16 Questions About Autoconf
***************************

Several questions about Autoconf come up occasionally.  Here some of
them are addressed.

* Menu:

* Distributing::                Distributing 'configure' scripts
* Why GNU m4::                  Why not use the standard M4?
* Bootstrapping::               Autoconf and GNU M4 require each other?
* Why Not Imake::               Why GNU uses 'configure' instead of Imake


File: autoconf.info,  Node: Distributing,  Next: Why GNU m4,  Prev: Questions,  Up: Questions

16.1 Distributing 'configure' Scripts
=====================================

     What are the restrictions on distributing 'configure'
     scripts that Autoconf generates?  How does that affect my
     programs that use them?

   There are no restrictions on how the configuration scripts that
Autoconf produces may be distributed or used.  In Autoconf version 1,
they were covered by the GNU General Public License.  We still encourage
software authors to distribute their work under terms like those of the
GPL, but doing so is not required to use Autoconf.

   Of the other files that might be used with 'configure', 'config.h.in'
is under whatever copyright you use for your 'configure.ac'.
'config.sub' and 'config.guess' have an exception to the GPL when they
are used with an Autoconf-generated 'configure' script, which permits
you to distribute them under the same terms as the rest of your package.
'install-sh' is from the X Consortium and is not copyrighted.


File: autoconf.info,  Node: Why GNU m4,  Next: Bootstrapping,  Prev: Distributing,  Up: Questions

16.2 Why Require GNU M4?
========================

     Why does Autoconf require GNU M4?

   Many M4 implementations have hard-coded limitations on the size and
number of macros that Autoconf exceeds.  They also lack several builtin
macros that it would be difficult to get along without in a
sophisticated application like Autoconf, including:

     builtin
     indir
     patsubst
     __file__
     __line__

   Autoconf requires version 1.4 or above of GNU M4 because it uses
frozen state files.

   Since only software maintainers need to use Autoconf, and since GNU
M4 is simple to configure and install, it seems reasonable to require
GNU M4 to be installed also.  Many maintainers of GNU and other free
software already have most of the GNU utilities installed, since they
prefer them.


File: autoconf.info,  Node: Bootstrapping,  Next: Why Not Imake,  Prev: Why GNU m4,  Up: Questions

16.3 How Can I Bootstrap?
=========================

     If Autoconf requires GNU M4 and GNU M4 has an Autoconf
     'configure' script, how do I bootstrap?  It seems like a chicken
     and egg problem!

   This is a misunderstanding.  Although GNU M4 does come with a
'configure' script produced by Autoconf, Autoconf is not required in
order to run the script and install GNU M4.  Autoconf is only required
if you want to change the M4 'configure' script, which few people have
to do (mainly its maintainer).


File: autoconf.info,  Node: Why Not Imake,  Prev: Bootstrapping,  Up: Questions

16.4 Why Not Imake?
===================

     Why not use Imake instead of 'configure' scripts?

   Several people have written addressing this question, so I include
adaptations of their explanations here.

   The following answer is based on one written by Richard Pixley:

     Autoconf generated scripts frequently work on machines that it has
     never been set up to handle before.  That is, it does a good job of
     inferring a configuration for a new system.  Imake cannot do this.

     Imake uses a common database of host specific data.  For X11, this
     makes sense because the distribution is made as a collection of
     tools, by one central authority who has control over the database.

     GNU tools are not released this way.  Each GNU tool has a
     maintainer; these maintainers are scattered across the world.
     Using a common database would be a maintenance nightmare.  Autoconf
     may appear to be this kind of database, but in fact it is not.
     Instead of listing host dependencies, it lists program
     requirements.

     If you view the GNU suite as a collection of native tools, then the
     problems are similar.  But the GNU development tools can be
     configured as cross tools in almost any host+target permutation.
     All of these configurations can be installed concurrently.  They
     can even be configured to share host independent files across
     hosts.  Imake doesn't address these issues.

     Imake templates are a form of standardization.  The GNU coding
     standards address the same issues without necessarily imposing the
     same restrictions.

   Here is some further explanation, written by Per Bothner:

     One of the advantages of Imake is that it easy to generate large
     Makefiles using 'cpp''s '#include' and macro mechanisms.  However,
     'cpp' is not programmable: it has limited conditional facilities,
     and no looping.  And 'cpp' cannot inspect its environment.

     All of these problems are solved by using 'sh' instead of 'cpp'.
     The shell is fully programmable, has macro substitution, can
     execute (or source) other shell scripts, and can inspect its
     environment.

   Paul Eggert elaborates more:

     With Autoconf, installers need not assume that Imake itself is
     already installed and working well.  This may not seem like much of
     an advantage to people who are accustomed to Imake.  But on many
     hosts Imake is not installed or the default installation is not
     working well, and requiring Imake to install a package hinders the
     acceptance of that package on those hosts.  For example, the Imake
     template and configuration files might not be installed properly on
     a host, or the Imake build procedure might wrongly assume that all
     source files are in one big directory tree, or the Imake
     configuration might assume one compiler whereas the package or the
     installer needs to use another, or there might be a version
     mismatch between the Imake expected by the package and the Imake
     supported by the host.  These problems are much rarer with
     Autoconf, where each package comes with its own independent
     configuration processor.

     Also, Imake often suffers from unexpected interactions between
     'make' and the installer's C preprocessor.  The fundamental problem
     here is that the C preprocessor was designed to preprocess C
     programs, not 'Makefile's.  This is much less of a problem with
     Autoconf, which uses the general-purpose preprocessor 'm4', and
     where the package's author (rather than the installer) does the
     preprocessing in a standard way.

   Finally, Mark Eichin notes:

     Imake isn't all that extensible, either.  In order to add new
     features to Imake, you need to provide your own project template,
     and duplicate most of the features of the existing one.  This means
     that for a sophisticated project, using the vendor-provided Imake
     templates fails to provide any leverage--since they don't cover
     anything that your own project needs (unless it is an X11 program).

     On the other side, though:

     The one advantage that Imake has over 'configure': 'Imakefile's
     tend to be much shorter (likewise, less redundant) than
     'Makefile.in's.  There is a fix to this, however--at least for the
     Kerberos V5 tree, we've modified things to call in common 'post.in'
     and 'pre.in' 'Makefile' fragments for the entire tree.  This means
     that a lot of common things don't have to be duplicated, even
     though they normally are in 'configure' setups.


File: autoconf.info,  Node: History,  Next: Environment Variable Index,  Prev: Questions,  Up: Top

17 History of Autoconf
**********************

You may be wondering, Why was Autoconf originally written?  How did it
get into its present form?  (Why does it look like gorilla spit?)  If
you're not wondering, then this chapter contains no information useful
to you, and you might as well skip it.  If you _are_ wondering, then let
there be light...

* Menu:

* Genesis::                     Prehistory and naming of 'configure'
* Exodus::                      The plagues of M4 and Perl
* Leviticus::                   The priestly code of portability arrives
* Numbers::                     Growth and contributors
* Deuteronomy::                 Approaching the promises of easy configuration


File: autoconf.info,  Node: Genesis,  Next: Exodus,  Prev: History,  Up: History

17.1 Genesis
============

In June 1991 I was maintaining many of the GNU utilities for the Free
Software Foundation.  As they were ported to more platforms and more
programs were added, the number of '-D' options that users had to select
in the 'Makefile' (around 20) became burdensome.  Especially for me--I
had to test each new release on a bunch of different systems.  So I
wrote a little shell script to guess some of the correct settings for
the fileutils package, and released it as part of fileutils 2.0.  That
'configure' script worked well enough that the next month I adapted it
(by hand) to create similar 'configure' scripts for several other GNU
utilities packages.  Brian Berliner also adapted one of my scripts for
his CVS revision control system.

   Later that summer, I learned that Richard Stallman and Richard Pixley
were developing similar scripts to use in the GNU compiler tools; so I
adapted my 'configure' scripts to support their evolving interface:
using the file name 'Makefile.in' as the templates; adding '+srcdir',
the first option (of many); and creating 'config.status' files.


File: autoconf.info,  Node: Exodus,  Next: Leviticus,  Prev: Genesis,  Up: History

17.2 Exodus
===========

As I got feedback from users, I incorporated many improvements, using
Emacs to search and replace, cut and paste, similar changes in each of
the scripts.  As I adapted more GNU utilities packages to use
'configure' scripts, updating them all by hand became impractical.  Rich
Murphey, the maintainer of the GNU graphics utilities, sent me mail
saying that the 'configure' scripts were great, and asking if I had a
tool for generating them that I could send him.  No, I thought, but I
should!  So I started to work out how to generate them.  And the journey
from the slavery of hand-written 'configure' scripts to the abundance
and ease of Autoconf began.

   Cygnus 'configure', which was being developed at around that time, is
table driven; it is meant to deal mainly with a discrete number of
system types with a small number of mainly unguessable features (such as
details of the object file format).  The automatic configuration system
that Brian Fox had developed for Bash takes a similar approach.  For
general use, it seems to me a hopeless cause to try to maintain an
up-to-date database of which features each variant of each operating
system has.  It's easier and more reliable to check for most features on
the fly--especially on hybrid systems that people have hacked on locally
or that have patches from vendors installed.

   I considered using an architecture similar to that of Cygnus
'configure', where there is a single 'configure' script that reads
pieces of 'configure.in' when run.  But I didn't want to have to
distribute all of the feature tests with every package, so I settled on
having a different 'configure' made from each 'configure.in' by a
preprocessor.  That approach also offered more control and flexibility.

   I looked briefly into using the Metaconfig package, by Larry Wall,
Harlan Stenn, and Raphael Manfredi, but I decided not to for several
reasons.  The 'Configure' scripts it produces are interactive, which I
find quite inconvenient; I didn't like the ways it checked for some
features (such as library functions); I didn't know that it was still
being maintained, and the 'Configure' scripts I had seen didn't work on
many modern systems (such as System V R4 and NeXT); it wasn't very
flexible in what it could do in response to a feature's presence or
absence; I found it confusing to learn; and it was too big and complex
for my needs (I didn't realize then how much Autoconf would eventually
have to grow).

   I considered using Perl to generate my style of 'configure' scripts,
but decided that M4 was better suited to the job of simple textual
substitutions: it gets in the way less, because output is implicit.
Plus, everyone already has it.  (Initially I didn't rely on the GNU
extensions to M4.)  Also, some of my friends at the University of
Maryland had recently been putting M4 front ends on several programs,
including 'tvtwm', and I was interested in trying out a new language.


File: autoconf.info,  Node: Leviticus,  Next: Numbers,  Prev: Exodus,  Up: History

17.3 Leviticus
==============

Since my 'configure' scripts determine the system's capabilities
automatically, with no interactive user intervention, I decided to call
the program that generates them Autoconfig.  But with a version number
tacked on, that name would be too long for old UNIX file systems, so I
shortened it to Autoconf.

   In the fall of 1991 I called together a group of fellow questers
after the Holy Grail of portability (er, that is, alpha testers) to give
me feedback as I encapsulated pieces of my handwritten scripts in M4
macros and continued to add features and improve the techniques used in
the checks.  Prominent among the testers were François Pinard, who came
up with the idea of making an 'autoconf' shell script to run 'm4' and
check for unresolved macro calls; Richard Pixley, who suggested running
the compiler instead of searching the file system to find include files
and symbols, for more accurate results; Karl Berry, who got Autoconf to
configure TeX and added the macro index to the documentation; and Ian
Lance Taylor, who added support for creating a C header file as an
alternative to putting '-D' options in a 'Makefile', so he could use
Autoconf for his UUCP package.  The alpha testers cheerfully adjusted
their files again and again as the names and calling conventions of the
Autoconf macros changed from release to release.  They all contributed
many specific checks, great ideas, and bug fixes.


File: autoconf.info,  Node: Numbers,  Next: Deuteronomy,  Prev: Leviticus,  Up: History

17.4 Numbers
============

In July 1992, after months of alpha testing, I released Autoconf 1.0,
and converted many GNU packages to use it.  I was surprised by how
positive the reaction to it was.  More people started using it than I
could keep track of, including people working on software that wasn't
part of the GNU Project (such as TCL, FSP, and Kerberos V5).  Autoconf
continued to improve rapidly, as many people using the 'configure'
scripts reported problems they encountered.

   Autoconf turned out to be a good torture test for M4 implementations.
UNIX 'm4' started to dump core because of the length of the macros that
Autoconf defined, and several bugs showed up in GNU 'm4' as well.
Eventually, we realized that we needed to use some features that only
GNU M4 has.  4.3BSD 'm4', in particular, has an impoverished set of
builtin macros; the System V version is better, but still doesn't
provide everything we need.

   More development occurred as people put Autoconf under more stresses
(and to uses I hadn't anticipated).  Karl Berry added checks for X11.
david zuhn contributed C++ support.  François Pinard made it diagnose
invalid arguments.  Jim Blandy bravely coerced it into configuring GNU
Emacs, laying the groundwork for several later improvements.  Roland
McGrath got it to configure the GNU C Library, wrote the 'autoheader'
script to automate the creation of C header file templates, and added a
'--verbose' option to 'configure'.  Noah Friedman added the
'--autoconf-dir' option and 'AC_MACRODIR' environment variable.  (He
also coined the term "autoconfiscate" to mean "adapt a software package
to use Autoconf".)  Roland and Noah improved the quoting protection in
'AC_DEFINE' and fixed many bugs, especially when I got sick of dealing
with portability problems from February through June, 1993.


File: autoconf.info,  Node: Deuteronomy,  Prev: Numbers,  Up: History

17.5 Deuteronomy
================

A long wish list for major features had accumulated, and the effect of
several years of patching by various people had left some residual
cruft.  In April 1994, while working for Cygnus Support, I began a major
revision of Autoconf.  I added most of the features of the Cygnus
'configure' that Autoconf had lacked, largely by adapting the relevant
parts of Cygnus 'configure' with the help of david zuhn and Ken Raeburn.
These features include support for using 'config.sub', 'config.guess',
'--host', and '--target'; making links to files; and running 'configure'
scripts in subdirectories.  Adding these features enabled Ken to convert
GNU 'as', and Rob Savoye to convert DejaGNU, to using Autoconf.

   I added more features in response to other peoples' requests.  Many
people had asked for 'configure' scripts to share the results of the
checks between runs, because (particularly when configuring a large
source tree, like Cygnus does) they were frustratingly slow.  Mike
Haertel suggested adding site-specific initialization scripts.  People
distributing software that had to unpack on MS-DOS asked for a way to
override the '.in' extension on the file names, which produced file
names like 'config.h.in' containing two dots.  Jim Avera did an
extensive examination of the problems with quoting in 'AC_DEFINE' and
'AC_SUBST'; his insights led to significant improvements.  Richard
Stallman asked that compiler output be sent to 'config.log' instead of
'/dev/null', to help people debug the Emacs 'configure' script.

   I made some other changes because of my dissatisfaction with the
quality of the program.  I made the messages showing results of the
checks less ambiguous, always printing a result.  I regularized the
names of the macros and cleaned up coding style inconsistencies.  I
added some auxiliary utilities that I had developed to help convert
source code packages to use Autoconf.  With the help of François Pinard,
I made the macros not interrupt each others' messages.  (That feature
revealed some performance bottlenecks in GNU 'm4', which he hastily
corrected!)  I reorganized the documentation around problems people want
to solve.  And I began a test suite, because experience had shown that
Autoconf has a pronounced tendency to regress when we change it.

   Again, several alpha testers gave invaluable feedback, especially
François Pinard, Jim Meyering, Karl Berry, Rob Savoye, Ken Raeburn, and
Mark Eichin.

   Finally, version 2.0 was ready.  And there was much rejoicing.  (And
I have free time again.  I think.  Yeah, right.)


File: autoconf.info,  Node: Environment Variable Index,  Next: Output Variable Index,  Prev: History,  Up: Top

Environment Variable Index
**************************

This is an alphabetical list of the environment variables that Autoconf
checks.

[index]
* Menu:

* AC_MACRODIR:                           autoscan Invocation.  (line 54)
* AC_MACRODIR <1>:                       autoconf Invocation.  (line 45)
* AC_MACRODIR <2>:                       autoreconf Invocation.
                                                               (line 77)
* AC_MACRODIR <3>:                       autoheader Invocation.
                                                               (line 62)
* AC_MACRODIR <4>:                       autoupdate Invocation.
                                                               (line 42)
* CDPATH:                                Special Shell Variables.
                                                               (line 13)
* CONFIG_COMMANDS:                       Obsolete config.status Use.
                                                               (line 11)
* CONFIG_FILES:                          Obsolete config.status Use.
                                                               (line 15)
* CONFIG_HEADERS:                        Obsolete config.status Use.
                                                               (line 20)
* CONFIG_LINKS:                          Obsolete config.status Use.
                                                               (line 25)
* CONFIG_SHELL:                          config.status Invocation.
                                                               (line 75)
* CONFIG_SITE:                           Site Defaults.        (line 10)
* CONFIG_STATUS:                         config.status Invocation.
                                                               (line 79)
* IFS:                                   Special Shell Variables.
                                                               (line 45)
* LANG:                                  Special Shell Variables.
                                                               (line 59)
* LANGUAGE:                              Special Shell Variables.
                                                               (line 59)
* LC_ALL:                                Special Shell Variables.
                                                               (line 59)
* LC_COLLATE:                            Special Shell Variables.
                                                               (line 59)
* LC_CTYPE:                              Special Shell Variables.
                                                               (line 59)
* LC_MESSAGES:                           Special Shell Variables.
                                                               (line 59)
* LC_NUMERIC:                            Special Shell Variables.
                                                               (line 59)
* LC_TIME:                               Special Shell Variables.
                                                               (line 59)
* NULLCMD:                               Special Shell Variables.
                                                               (line 77)
* PATH_SEPARATOR:                        Special Shell Variables.
                                                               (line 88)
* RANDOM:                                Special Shell Variables.
                                                               (line 97)
* SIMPLE_BACKUP_SUFFIX:                  autoupdate Invocation.
                                                               (line 16)
* status:                                Special Shell Variables.
                                                               (line 84)
* WARNINGS:                              autoconf Invocation.  (line 65)
* WARNINGS <1>:                          autoheader Invocation.
                                                               (line 78)


File: autoconf.info,  Node: Output Variable Index,  Next: Preprocessor Symbol Index,  Prev: Environment Variable Index,  Up: Top

Output Variable Index
*********************

This is an alphabetical list of the variables that Autoconf can
substitute into files that it creates, typically one or more
'Makefile's.  *Note Setting Output Variables::, for more information on
how this is done.

[index]
* Menu:

* ALLOCA:                                Particular Functions.
                                                              (line  10)
* AWK:                                   Particular Programs. (line  10)
* bindir:                                Installation Directory Variables.
                                                              (line  12)
* build:                                 Canonicalizing.      (line  26)
* build_alias:                           Canonicalizing.      (line   9)
* build_cpu:                             Canonicalizing.      (line  26)
* build_os:                              Canonicalizing.      (line  26)
* build_vendor:                          Canonicalizing.      (line  26)
* CC:                                    C Compiler.          (line   7)
* CC <1>:                                C Compiler.          (line  34)
* CC <2>:                                C Compiler.          (line 156)
* CC <3>:                                System Services.     (line  44)
* CC <4>:                                UNIX Variants.       (line  18)
* CFLAGS:                                Preset Output Variables.
                                                              (line  15)
* CFLAGS <1>:                            C Compiler.          (line   7)
* configure_input:                       Preset Output Variables.
                                                              (line  22)
* CPP:                                   C Compiler.          (line  47)
* CPPFLAGS:                              Preset Output Variables.
                                                              (line  36)
* cross_compiling:                       Specifying Names.    (line  26)
* CXX:                                   C++ Compiler.        (line   7)
* CXXCPP:                                C++ Compiler.        (line  31)
* CXXFLAGS:                              Preset Output Variables.
                                                              (line  43)
* CXXFLAGS <1>:                          C++ Compiler.        (line   7)
* datadir:                               Installation Directory Variables.
                                                              (line  15)
* DEFS:                                  Preset Output Variables.
                                                              (line  50)
* ECHO_C:                                Preset Output Variables.
                                                              (line  60)
* ECHO_N:                                Preset Output Variables.
                                                              (line  60)
* ECHO_T:                                Preset Output Variables.
                                                              (line  60)
* EGREP:                                 Particular Programs. (line  16)
* exec_prefix:                           Installation Directory Variables.
                                                              (line  19)
* EXEEXT:                                Compilers and Preprocessors.
                                                              (line   6)
* EXEEXT <1>:                            Obsolete Macros.     (line 145)
* F77:                                   Fortran 77 Compiler. (line   7)
* FFLAGS:                                Preset Output Variables.
                                                              (line  72)
* FFLAGS <1>:                            Fortran 77 Compiler. (line   7)
* FGREP:                                 Particular Programs. (line  20)
* FLIBS:                                 Fortran 77 Compiler. (line  38)
* GETGROUPS_LIBS:                        Particular Functions.
                                                              (line  97)
* GETLOADAVG_LIBS:                       Particular Functions.
                                                              (line 103)
* GREP:                                  Particular Programs. (line  24)
* host:                                  Canonicalizing.      (line  34)
* host_alias:                            Canonicalizing.      (line   9)
* host_cpu:                              Canonicalizing.      (line  34)
* host_os:                               Canonicalizing.      (line  34)
* host_vendor:                           Canonicalizing.      (line  34)
* includedir:                            Installation Directory Variables.
                                                              (line  26)
* infodir:                               Installation Directory Variables.
                                                              (line  29)
* INSTALL:                               Particular Programs. (line  28)
* INSTALL_DATA:                          Particular Programs. (line  28)
* INSTALL_PROGRAM:                       Particular Programs. (line  28)
* INSTALL_SCRIPT:                        Particular Programs. (line  28)
* KMEM_GROUP:                            Particular Functions.
                                                              (line 103)
* LDFLAGS:                               Preset Output Variables.
                                                              (line  79)
* LEX:                                   Particular Programs. (line  57)
* LEXLIB:                                Particular Programs. (line  57)
* LEX_OUTPUT_ROOT:                       Particular Programs. (line  57)
* libdir:                                Installation Directory Variables.
                                                              (line  32)
* libexecdir:                            Installation Directory Variables.
                                                              (line  35)
* LIBOBJS:                               Particular Functions.
                                                              (line 103)
* LIBOBJS <1>:                           Particular Functions.
                                                              (line 160)
* LIBOBJS <2>:                           Particular Functions.
                                                              (line 167)
* LIBOBJS <3>:                           Generic Functions.   (line  44)
* LIBOBJS <4>:                           Generic Functions.   (line  84)
* LIBOBJS <5>:                           Particular Structures.
                                                              (line  17)
* LIBS:                                  Preset Output Variables.
                                                              (line  87)
* LIBS <1>:                              Obsolete Macros.     (line 408)
* LIBS <2>:                              Obsolete Macros.     (line 515)
* LN_S:                                  Particular Programs. (line  95)
* localstatedir:                         Installation Directory Variables.
                                                              (line  38)
* mandir:                                Installation Directory Variables.
                                                              (line  41)
* NEED_SETGID:                           Particular Functions.
                                                              (line 103)
* OBJEXT:                                Compilers and Preprocessors.
                                                              (line  10)
* OBJEXT <1>:                            Obsolete Macros.     (line 300)
* oldincludedir:                         Installation Directory Variables.
                                                              (line  44)
* POW_LIB:                               Particular Functions.
                                                              (line 216)
* prefix:                                Installation Directory Variables.
                                                              (line  47)
* program_transform_name:                Transforming Names.  (line  11)
* RANLIB:                                Particular Programs. (line 114)
* sbindir:                               Installation Directory Variables.
                                                              (line  52)
* SET_MAKE:                              Output.              (line  37)
* sharedstatedir:                        Installation Directory Variables.
                                                              (line  56)
* srcdir:                                Preset Output Variables.
                                                              (line  94)
* subdirs:                               Subdirectories.      (line  12)
* sysconfdir:                            Installation Directory Variables.
                                                              (line  60)
* target:                                Canonicalizing.      (line  46)
* target_alias:                          Canonicalizing.      (line   9)
* target_cpu:                            Canonicalizing.      (line  46)
* target_os:                             Canonicalizing.      (line  46)
* target_vendor:                         Canonicalizing.      (line  46)
* top_srcdir:                            Preset Output Variables.
                                                              (line  97)
* X_CFLAGS:                              System Services.     (line  26)
* X_EXTRA_LIBS:                          System Services.     (line  26)
* X_LIBS:                                System Services.     (line  26)
* X_PRE_LIBS:                            System Services.     (line  26)
* YACC:                                  Particular Programs. (line 118)


File: autoconf.info,  Node: Preprocessor Symbol Index,  Next: Autoconf Macro Index,  Prev: Output Variable Index,  Up: Top

Preprocessor Symbol Index
*************************

This is an alphabetical list of the C preprocessor symbols that the
Autoconf macros define.  To work with Autoconf, C source code needs to
use these names in '#if' directives.

[index]
* Menu:

* _ALL_SOURCE:                           UNIX Variants.       (line  13)
* _FILE_OFFSET_BITS:                     System Services.     (line  44)
* _LARGEFILE_SOURCE:                     Particular Functions.
                                                              (line  93)
* _LARGE_FILES:                          System Services.     (line  44)
* _MINIX:                                UNIX Variants.       (line  25)
* _POSIX_1_SOURCE:                       UNIX Variants.       (line  25)
* _POSIX_SOURCE:                         UNIX Variants.       (line  18)
* _POSIX_SOURCE <1>:                     UNIX Variants.       (line  25)
* _POSIX_VERSION:                        Particular Headers.  (line 130)
* __CHAR_UNSIGNED__:                     C Compiler.          (line 120)
* CLOSEDIR_VOID:                         Particular Functions.
                                                              (line  58)
* const:                                 C Compiler.          (line  73)
* C_ALLOCA:                              Particular Functions.
                                                              (line  10)
* C_GETLOADAVG:                          Particular Functions.
                                                              (line 103)
* DGUX:                                  Particular Functions.
                                                              (line 103)
* DIRENT:                                Obsolete Macros.     (line 126)
* F77_DUMMY_MAIN:                        Fortran 77 Compiler. (line  64)
* F77_FUNC:                              Fortran 77 Compiler. (line 115)
* F77_FUNC_:                             Fortran 77 Compiler. (line 115)
* F77_MAIN:                              Fortran 77 Compiler. (line 101)
* F77_NO_MINUS_C_MINUS_O:                Fortran 77 Compiler. (line  28)
* GETGROUPS_T:                           Particular Types.    (line  10)
* GETLODAVG_PRIVILEGED:                  Particular Functions.
                                                              (line 103)
* GETPGRP_VOID:                          Particular Functions.
                                                              (line 136)
* gid_t:                                 Particular Types.    (line  39)
* GWINSZ_IN_SYS_IOCTL:                   Particular Headers.  (line 167)
* HAVE_ALLOCA_H:                         Particular Functions.
                                                              (line  10)
* HAVE_CONFIG_H:                         Configuration Headers.
                                                              (line  25)
* HAVE_DECL_SYMBOL:                      Generic Declarations.
                                                              (line  23)
* HAVE_DIRENT_H:                         Particular Headers.  (line  10)
* HAVE_DOPRNT:                           Particular Functions.
                                                              (line 238)
* HAVE_FUNCTION:                         Generic Functions.   (line  25)
* HAVE_GETMNTENT:                        Particular Functions.
                                                              (line 131)
* HAVE_HEADER:                           Generic Headers.     (line  43)
* HAVE_LONG_DOUBLE:                      C Compiler.          (line 124)
* HAVE_LONG_FILE_NAMES:                  System Services.     (line  58)
* HAVE_LSTAT_EMPTY_STRING_BUG:           Particular Functions.
                                                              (line 196)
* HAVE_MMAP:                             Particular Functions.
                                                              (line 171)
* HAVE_NDIR_H:                           Particular Headers.  (line  10)
* HAVE_OBSTACK:                          Particular Functions.
                                                              (line 176)
* HAVE_RESTARTABLE_SYSCALLS:             Obsolete Macros.     (line 446)
* HAVE_STAT_EMPTY_STRING_BUG:            Particular Functions.
                                                              (line 196)
* HAVE_STRCOLL:                          Particular Functions.
                                                              (line 210)
* HAVE_STRERROR_R:                       Particular Functions.
                                                              (line 222)
* HAVE_STRFTIME:                         Particular Functions.
                                                              (line 230)
* HAVE_STRINGIZE:                        C Compiler.          (line 130)
* HAVE_STRUCT_STAT_ST_BLKSIZE:           Particular Structures.
                                                              (line   9)
* HAVE_STRUCT_STAT_ST_BLOCKS:            Particular Structures.
                                                              (line  17)
* HAVE_STRUCT_STAT_ST_RDEV:              Particular Structures.
                                                              (line  23)
* HAVE_ST_BLKSIZE:                       Particular Structures.
                                                              (line   9)
* HAVE_ST_BLOCKS:                        Particular Structures.
                                                              (line  17)
* HAVE_ST_RDEV:                          Particular Structures.
                                                              (line  23)
* HAVE_SYS_DIR_H:                        Particular Headers.  (line  10)
* HAVE_SYS_NDIR_H:                       Particular Headers.  (line  10)
* HAVE_SYS_WAIT_H:                       Particular Headers.  (line 112)
* HAVE_TM_ZONE:                          Particular Structures.
                                                              (line  36)
* HAVE_TZNAME:                           Particular Structures.
                                                              (line  36)
* HAVE_UTIME_NULL:                       Particular Functions.
                                                              (line 234)
* HAVE_VFORK_H:                          Particular Functions.
                                                              (line  71)
* HAVE_VPRINTF:                          Particular Functions.
                                                              (line 238)
* HAVE_WAIT3:                            Obsolete Macros.     (line 166)
* HAVE_WORKING_FORK:                     Particular Functions.
                                                              (line  71)
* HAVE_WORKING_STRERROR_R:               Particular Functions.
                                                              (line 222)
* HAVE_WORKING_VFORK:                    Particular Functions.
                                                              (line  71)
* inline:                                C Compiler.          (line 115)
* INT_16_BITS:                           Obsolete Macros.     (line 217)
* LONG_64_BITS:                          Obsolete Macros.     (line 268)
* LSTAT_FOLLOWS_SLASHED_SYMLINK:         Particular Functions.
                                                              (line 143)
* MAJOR_IN_MKDEV:                        Particular Headers.  (line  46)
* MAJOR_IN_SYSMACROS:                    Particular Headers.  (line  46)
* mode_t:                                Particular Types.    (line  14)
* NDIR:                                  Obsolete Macros.     (line 126)
* NEED_MEMORY_H:                         Obsolete Macros.     (line 281)
* NEED_SETGID:                           Particular Functions.
                                                              (line 103)
* NLIST_NAME_UNION:                      Particular Functions.
                                                              (line 103)
* NLIST_STRUCT:                          Particular Functions.
                                                              (line 103)
* NO_MINUS_C_MINUS_O:                    C Compiler.          (line  26)
* off_t:                                 Particular Types.    (line  17)
* PARAMS:                                C Compiler.          (line 137)
* pid_t:                                 Particular Types.    (line  20)
* PROTOTYPES:                            C Compiler.          (line 137)
* RETSIGTYPE:                            Particular Types.    (line  23)
* SELECT_TYPE_ARG1:                      Particular Functions.
                                                              (line 180)
* SELECT_TYPE_ARG234:                    Particular Functions.
                                                              (line 180)
* SELECT_TYPE_ARG5:                      Particular Functions.
                                                              (line 180)
* SETPGRP_VOID:                          Particular Functions.
                                                              (line 188)
* SETVBUF_REVERSED:                      Particular Functions.
                                                              (line 205)
* size_t:                                Particular Types.    (line  36)
* STDC_HEADERS:                          Particular Headers.  (line  57)
* SVR4:                                  Particular Functions.
                                                              (line 103)
* SYSDIR:                                Obsolete Macros.     (line 126)
* SYSNDIR:                               Obsolete Macros.     (line 126)
* SYS_SIGLIST_DECLARED:                  Particular Declarations.
                                                              (line   9)
* TIME_WITH_SYS_TIME:                    Particular Headers.  (line 146)
* TM_IN_SYS_TIME:                        Particular Structures.
                                                              (line  31)
* uid_t:                                 Particular Types.    (line  39)
* UMAX:                                  Particular Functions.
                                                              (line 103)
* UMAX4_3:                               Particular Functions.
                                                              (line 103)
* USG:                                   Obsolete Macros.     (line 482)
* vfork:                                 Particular Functions.
                                                              (line  71)
* volatile:                              C Compiler.          (line  98)
* WORDS_BIGENDIAN:                       C Compiler.          (line  68)
* X_DISPLAY_MISSING:                     System Services.     (line  26)
* YYTEXT_POINTER:                        Particular Programs. (line  57)


File: autoconf.info,  Node: Autoconf Macro Index,  Next: M4 Macro Index,  Prev: Preprocessor Symbol Index,  Up: Top

Autoconf Macro Index
********************

This is an alphabetical list of the Autoconf macros.  To make the list
easier to use, the macros are listed without their preceding 'AC_'.

[index]
* Menu:

* AH_BOTTOM:                             Autoheader Macros.   (line  56)
* AH_TEMPLATE:                           Autoheader Macros.   (line  32)
* AH_TOP:                                Autoheader Macros.   (line  53)
* AH_VERBATIM:                           Autoheader Macros.   (line  18)
* AIX:                                   UNIX Variants.       (line  13)
* ALLOCA:                                Obsolete Macros.     (line  20)
* ARG_ARRAY:                             Obsolete Macros.     (line  23)
* ARG_ENABLE:                            Package Options.     (line  40)
* ARG_PROGRAM:                           Transforming Names.  (line  11)
* ARG_VAR:                               Setting Output Variables.
                                                              (line  57)
* ARG_WITH:                              External Software.   (line  41)
* AU_DEFUN:                              Obsoleting Macros.   (line  18)
* BEFORE:                                Suggested Ordering.  (line  28)
* BOTTOM:                                Autoheader Macros.   (line  56)
* CACHE_CHECK:                           Caching Results.     (line  29)
* CACHE_LOAD:                            Cache Checkpointing. (line  13)
* CACHE_SAVE:                            Cache Checkpointing. (line  17)
* CACHE_VAL:                             Caching Results.     (line  15)
* CANONICAL_BUILD:                       Canonicalizing.      (line  26)
* CANONICAL_HOST:                        Canonicalizing.      (line  34)
* CANONICAL_SYSTEM:                      Obsolete Macros.     (line  29)
* CANONICAL_TARGET:                      Canonicalizing.      (line  46)
* CHAR_UNSIGNED:                         Obsolete Macros.     (line  39)
* CHECKING:                              Obsolete Macros.     (line  89)
* CHECK_DECL:                            Generic Declarations.
                                                              (line  11)
* CHECK_DECLS:                           Generic Declarations.
                                                              (line  23)
* CHECK_FILE:                            Files.               (line  13)
* CHECK_FILES:                           Files.               (line  19)
* CHECK_FUNC:                            Generic Functions.   (line  15)
* CHECK_FUNCS:                           Generic Functions.   (line  25)
* CHECK_HEADER:                          Generic Headers.     (line  13)
* CHECK_HEADERS:                         Generic Headers.     (line  43)
* CHECK_LIB:                             Libraries.           (line  11)
* CHECK_MEMBER:                          Generic Structures.  (line  11)
* CHECK_MEMBERS:                         Generic Structures.  (line  25)
* CHECK_PROG:                            Generic Programs.    (line  23)
* CHECK_PROGS:                           Generic Programs.    (line  33)
* CHECK_SIZEOF:                          Generic Compiler Characteristics.
                                                              (line   7)
* CHECK_TOOL:                            Generic Programs.    (line  43)
* CHECK_TOOLS:                           Generic Programs.    (line  54)
* CHECK_TYPE:                            Generic Types.       (line  11)
* CHECK_TYPE <1>:                        Obsolete Macros.     (line  42)
* CHECK_TYPES:                           Generic Types.       (line  16)
* COMPILE_CHECK:                         Obsolete Macros.     (line  93)
* CONFIG_AUX_DIR:                        Input.               (line  29)
* CONFIG_COMMANDS:                       Configuration Commands.
                                                              (line  13)
* CONFIG_FILES:                          Configuration Files. (line   9)
* CONFIG_HEADERS:                        Configuration Headers.
                                                              (line  25)
* CONFIG_LINKS:                          Configuration Links. (line  12)
* CONFIG_SRCDIR:                         Input.               (line  16)
* CONFIG_SUBDIRS:                        Subdirectories.      (line  12)
* CONST:                                 Obsolete Macros.     (line 100)
* COPYRIGHT:                             Notices.             (line  21)
* CROSS_CHECK:                           Obsolete Macros.     (line 103)
* CYGWIN:                                Obsolete Macros.     (line 107)
* C_BIGENDIAN:                           C Compiler.          (line  68)
* C_CHAR_UNSIGNED:                       C Compiler.          (line 120)
* C_CONST:                               C Compiler.          (line  73)
* C_CROSS:                               Obsolete Macros.     (line  26)
* C_INLINE:                              C Compiler.          (line 115)
* C_LONG_DOUBLE:                         C Compiler.          (line 124)
* C_PROTOTYPES:                          C Compiler.          (line 137)
* C_STRINGIZE:                           C Compiler.          (line 130)
* C_VOLATILE:                            C Compiler.          (line  98)
* DECL_SYS_SIGLIST:                      Particular Declarations.
                                                              (line   9)
* DECL_YYTEXT:                           Obsolete Macros.     (line 123)
* DEFINE:                                Defining Symbols.    (line  29)
* DEFINE_UNQUOTED:                       Defining Symbols.    (line  45)
* DEFUN:                                 Macro Definitions.   (line   6)
* DEFUN <1>:                             Obsoleting Macros.   (line  18)
* DIAGNOSE:                              Reporting Messages.  (line  11)
* DIR_HEADER:                            Obsolete Macros.     (line 126)
* DYNIX_SEQ:                             Obsolete Macros.     (line 137)
* EGREP_CPP:                             Examining Declarations.
                                                              (line  46)
* EGREP_HEADER:                          Examining Declarations.
                                                              (line  29)
* EMXOS2:                                Obsolete Macros.     (line 150)
* ENABLE:                                Package Options.     (line  57)
* ERROR:                                 Obsolete Macros.     (line 154)
* EXEEXT:                                Obsolete Macros.     (line 145)
* F77_DUMMY_MAIN:                        Fortran 77 Compiler. (line  64)
* F77_FUNC:                              Fortran 77 Compiler. (line 169)
* F77_LIBRARY_LDFLAGS:                   Fortran 77 Compiler. (line  38)
* F77_MAIN:                              Fortran 77 Compiler. (line 101)
* F77_WRAPPERS:                          Fortran 77 Compiler. (line 115)
* FATAL:                                 Reporting Messages.  (line  33)
* FIND_X:                                Obsolete Macros.     (line 157)
* FIND_XTRA:                             Obsolete Macros.     (line 160)
* FUNC_ALLOCA:                           Particular Functions.
                                                              (line  10)
* FUNC_CHECK:                            Obsolete Macros.     (line 163)
* FUNC_CHOWN:                            Particular Functions.
                                                              (line  54)
* FUNC_CLOSEDIR_VOID:                    Particular Functions.
                                                              (line  58)
* FUNC_ERROR_AT_LINE:                    Particular Functions.
                                                              (line  63)
* FUNC_FNMATCH:                          Particular Functions.
                                                              (line  67)
* FUNC_FORK:                             Particular Functions.
                                                              (line  71)
* FUNC_FSEEKO:                           Particular Functions.
                                                              (line  93)
* FUNC_GETGROUPS:                        Particular Functions.
                                                              (line  97)
* FUNC_GETLOADAVG:                       Particular Functions.
                                                              (line 103)
* FUNC_GETMNTENT:                        Particular Functions.
                                                              (line 131)
* FUNC_GETPGRP:                          Particular Functions.
                                                              (line 136)
* FUNC_LSTAT:                            Particular Functions.
                                                              (line 196)
* FUNC_LSTAT_FOLLOWS_SLASHED_SYMLINK:    Particular Functions.
                                                              (line 143)
* FUNC_MALLOC:                           Particular Functions.
                                                              (line 156)
* FUNC_MEMCMP:                           Particular Functions.
                                                              (line 160)
* FUNC_MKTIME:                           Particular Functions.
                                                              (line 167)
* FUNC_MMAP:                             Particular Functions.
                                                              (line 171)
* FUNC_OBSTACK:                          Particular Functions.
                                                              (line 176)
* FUNC_SELECT_ARGTYPES:                  Particular Functions.
                                                              (line 180)
* FUNC_SETPGRP:                          Particular Functions.
                                                              (line 188)
* FUNC_SETVBUF_REVERSED:                 Particular Functions.
                                                              (line 205)
* FUNC_STAT:                             Particular Functions.
                                                              (line 196)
* FUNC_STRCOLL:                          Particular Functions.
                                                              (line 210)
* FUNC_STRERROR_R:                       Particular Functions.
                                                              (line 222)
* FUNC_STRFTIME:                         Particular Functions.
                                                              (line 230)
* FUNC_STRTOD:                           Particular Functions.
                                                              (line 216)
* FUNC_UTIME_NULL:                       Particular Functions.
                                                              (line 234)
* FUNC_VPRINTF:                          Particular Functions.
                                                              (line 238)
* FUNC_WAIT3:                            Obsolete Macros.     (line 166)
* GCC_TRADITIONAL:                       Obsolete Macros.     (line 175)
* GETGROUPS_T:                           Obsolete Macros.     (line 178)
* GETLOADAVG:                            Obsolete Macros.     (line 181)
* HAVE_FUNCS:                            Obsolete Macros.     (line 184)
* HAVE_HEADERS:                          Obsolete Macros.     (line 187)
* HAVE_LIBRARY:                          Obsolete Macros.     (line 191)
* HAVE_POUNDBANG:                        Obsolete Macros.     (line 198)
* HEADER_CHECK:                          Obsolete Macros.     (line 201)
* HEADER_DIRENT:                         Particular Headers.  (line  10)
* HEADER_EGREP:                          Obsolete Macros.     (line 204)
* HEADER_MAJOR:                          Particular Headers.  (line  46)
* HEADER_STAT:                           Particular Headers.  (line  51)
* HEADER_STDC:                           Particular Headers.  (line  57)
* HEADER_SYS_WAIT:                       Particular Headers.  (line 112)
* HEADER_TIME:                           Particular Headers.  (line 146)
* HEADER_TIOCGWINSZ:                     Particular Headers.  (line 167)
* HELP_STRING:                           Pretty Help Strings. (line  14)
* INIT:                                  Input.               (line  10)
* INIT <1>:                              Obsolete Macros.     (line 207)
* INLINE:                                Obsolete Macros.     (line 214)
* INT_16_BITS:                           Obsolete Macros.     (line 217)
* IRIX_SUN:                              Obsolete Macros.     (line 221)
* ISC_POSIX:                             UNIX Variants.       (line  18)
* LANG_C:                                Obsolete Macros.     (line 235)
* LANG_CPLUSPLUS:                        Obsolete Macros.     (line 238)
* LANG_FORTRAN77:                        Obsolete Macros.     (line 241)
* LANG_POP:                              Language Choice.     (line  37)
* LANG_PUSH:                             Language Choice.     (line  32)
* LANG_RESTORE:                          Obsolete Macros.     (line 244)
* LANG_SAVE:                             Obsolete Macros.     (line 249)
* LIBOBJ:                                Generic Functions.   (line  44)
* LIBSOURCE:                             Generic Functions.   (line  52)
* LIBSOURCES:                            Generic Functions.   (line  76)
* LINK_FILES:                            Obsolete Macros.     (line 253)
* LN_S:                                  Obsolete Macros.     (line 265)
* LONG_64_BITS:                          Obsolete Macros.     (line 268)
* LONG_DOUBLE:                           Obsolete Macros.     (line 272)
* LONG_FILE_NAMES:                       Obsolete Macros.     (line 275)
* MAJOR_HEADER:                          Obsolete Macros.     (line 278)
* MEMORY_H:                              Obsolete Macros.     (line 281)
* MINGW32:                               Obsolete Macros.     (line 287)
* MINIX:                                 UNIX Variants.       (line  25)
* MINUS_C_MINUS_O:                       Obsolete Macros.     (line 291)
* MMAP:                                  Obsolete Macros.     (line 294)
* MODE_T:                                Obsolete Macros.     (line 297)
* MSG_CHECKING:                          Printing Messages.   (line  23)
* MSG_ERROR:                             Printing Messages.   (line  54)
* MSG_NOTICE:                            Printing Messages.   (line  44)
* MSG_RESULT:                            Printing Messages.   (line  34)
* MSG_WARN:                              Printing Messages.   (line  64)
* OBJEXT:                                Obsolete Macros.     (line 300)
* OBSOLETE:                              Obsolete Macros.     (line 306)
* OFF_T:                                 Obsolete Macros.     (line 321)
* OUTPUT:                                Output.              (line  12)
* OUTPUT <1>:                            Obsolete Macros.     (line 324)
* OUTPUT_COMMANDS:                       Obsolete Macros.     (line 346)
* OUTPUT_COMMANDS_POST:                  Configuration Commands.
                                                              (line  39)
* OUTPUT_COMMANDS_PRE:                   Configuration Commands.
                                                              (line  30)
* PATH_PROG:                             Generic Programs.    (line  66)
* PATH_PROGS:                            Generic Programs.    (line  71)
* PATH_TOOL:                             Generic Programs.    (line  76)
* PATH_X:                                System Services.     (line  10)
* PATH_XTRA:                             System Services.     (line  26)
* PID_T:                                 Obsolete Macros.     (line 375)
* PREFIX:                                Obsolete Macros.     (line 378)
* PREFIX_DEFAULT:                        Default Prefix.      (line  16)
* PREFIX_PROGRAM:                        Default Prefix.      (line  25)
* PREREQ:                                Notices.             (line  10)
* PROGRAMS_CHECK:                        Obsolete Macros.     (line 381)
* PROGRAMS_PATH:                         Obsolete Macros.     (line 384)
* PROGRAM_CHECK:                         Obsolete Macros.     (line 387)
* PROGRAM_EGREP:                         Obsolete Macros.     (line 390)
* PROGRAM_PATH:                          Obsolete Macros.     (line 393)
* PROG_AWK:                              Particular Programs. (line  10)
* PROG_CC:                               C Compiler.          (line   7)
* PROG_CC_C_O:                           C Compiler.          (line  26)
* PROG_CC_STDC:                          C Compiler.          (line  34)
* PROG_CPP:                              C Compiler.          (line  47)
* PROG_CXX:                              C++ Compiler.        (line   7)
* PROG_CXXCPP:                           C++ Compiler.        (line  31)
* PROG_F77_C_O:                          Fortran 77 Compiler. (line  28)
* PROG_FORTRAN:                          Fortran 77 Compiler. (line   7)
* PROG_GCC_TRADITIONAL:                  C Compiler.          (line 156)
* PROG_INSTALL:                          Particular Programs. (line  28)
* PROG_LEX:                              Particular Programs. (line  57)
* PROG_LN_S:                             Particular Programs. (line  95)
* PROG_MAKE_SET:                         Output.              (line  37)
* PROG_RANLIB:                           Particular Programs. (line 114)
* PROG_YACC:                             Particular Programs. (line 118)
* REMOTE_TAPE:                           Obsolete Macros.     (line 396)
* REPLACE_FUNCS:                         Generic Functions.   (line  84)
* REQUIRE:                               Prerequisite Macros. (line  17)
* REQUIRE_CPP:                           Language Choice.     (line  50)
* RESTARTABLE_SYSCALLS:                  Obsolete Macros.     (line 399)
* RETSIGTYPE:                            Obsolete Macros.     (line 402)
* REVISION:                              Notices.             (line  29)
* RSH:                                   Obsolete Macros.     (line 405)
* SCO_INTL:                              Obsolete Macros.     (line 408)
* SEARCH_LIBS:                           Libraries.           (line  41)
* SETVBUF_REVERSED:                      Obsolete Macros.     (line 416)
* SET_MAKE:                              Obsolete Macros.     (line 419)
* SIZEOF_TYPE:                           Obsolete Macros.     (line 422)
* SIZE_T:                                Obsolete Macros.     (line 425)
* STAT_MACROS_BROKEN:                    Particular Headers.  (line  51)
* STAT_MACROS_BROKEN <1>:                Obsolete Macros.     (line 428)
* STDC_HEADERS:                          Obsolete Macros.     (line 431)
* STRCOLL:                               Obsolete Macros.     (line 434)
* STRUCT_ST_BLKSIZE:                     Particular Structures.
                                                              (line   9)
* STRUCT_ST_BLOCKS:                      Particular Structures.
                                                              (line  17)
* STRUCT_ST_RDEV:                        Particular Structures.
                                                              (line  23)
* STRUCT_TIMEZONE:                       Particular Structures.
                                                              (line  36)
* STRUCT_TM:                             Particular Structures.
                                                              (line  31)
* ST_BLKSIZE:                            Obsolete Macros.     (line 437)
* ST_BLOCKS:                             Obsolete Macros.     (line 440)
* ST_RDEV:                               Obsolete Macros.     (line 443)
* SUBST:                                 Setting Output Variables.
                                                              (line  13)
* SUBST_FILE:                            Setting Output Variables.
                                                              (line  23)
* SYS_INTERPRETER:                       System Services.     (line  37)
* SYS_LARGEFILE:                         System Services.     (line  44)
* SYS_LONG_FILE_NAMES:                   System Services.     (line  58)
* SYS_POSIX_TERMIOS:                     System Services.     (line  62)
* SYS_RESTARTABLE_SYSCALLS:              Obsolete Macros.     (line 446)
* SYS_SIGLIST_DECLARED:                  Obsolete Macros.     (line 461)
* TEMPLATE:                              Autoheader Macros.   (line  32)
* TEST_CPP:                              Obsolete Macros.     (line 464)
* TEST_PROGRAM:                          Obsolete Macros.     (line 467)
* TIMEZONE:                              Obsolete Macros.     (line 470)
* TIME_WITH_SYS_TIME:                    Obsolete Macros.     (line 473)
* TOP:                                   Autoheader Macros.   (line  53)
* TRY_COMPILE:                           Examining Syntax.    (line  14)
* TRY_CPP:                               Examining Declarations.
                                                              (line  11)
* TRY_LINK:                              Examining Libraries. (line  33)
* TRY_LINK_FUNC:                         Examining Libraries. (line  51)
* TRY_RUN:                               Test Programs.       (line  11)
* TYPE_GETGROUPS:                        Particular Types.    (line  10)
* TYPE_MODE_T:                           Particular Types.    (line  14)
* TYPE_OFF_T:                            Particular Types.    (line  17)
* TYPE_PID_T:                            Particular Types.    (line  20)
* TYPE_SIGNAL:                           Particular Types.    (line  23)
* TYPE_SIZE_T:                           Particular Types.    (line  36)
* TYPE_UID_T:                            Particular Types.    (line  39)
* UID_T:                                 Obsolete Macros.     (line 476)
* UNISTD_H:                              Obsolete Macros.     (line 479)
* USG:                                   Obsolete Macros.     (line 482)
* UTIME_NULL:                            Obsolete Macros.     (line 487)
* VALIDATE_CACHED_SYSTEM_TUPLE:          Obsolete Macros.     (line 490)
* VERBATIM:                              Autoheader Macros.   (line  18)
* VERBOSE:                               Obsolete Macros.     (line 497)
* VFORK:                                 Obsolete Macros.     (line 500)
* VPRINTF:                               Obsolete Macros.     (line 503)
* WAIT3:                                 Obsolete Macros.     (line 506)
* WARN:                                  Obsolete Macros.     (line 509)
* WARNING:                               Reporting Messages.  (line  29)
* WITH:                                  External Software.   (line  67)
* WORDS_BIGENDIAN:                       Obsolete Macros.     (line 512)
* XENIX_DIR:                             Obsolete Macros.     (line 515)
* YYTEXT_POINTER:                        Obsolete Macros.     (line 530)


File: autoconf.info,  Node: M4 Macro Index,  Next: Concept Index,  Prev: Autoconf Macro Index,  Up: Top

M4 Macro Index
**************

This is an alphabetical list of the M4, M4sugar, and M4sh macros.  To
make the list easier to use, the macros are listed without their
preceding 'm4_' or 'AS_'.

[index]
* Menu:

* defn:                                  Redefined M4 Macros.  (line 14)
* defn <1>:                              Redefined M4 Macros.  (line 26)
* pattern_allow:                         Forbidden Patterns.   (line 28)
* pattern_forbid:                        Forbidden Patterns.   (line 15)
* undefine:                              Redefined M4 Macros.  (line 18)


File: autoconf.info,  Node: Concept Index,  Prev: M4 Macro Index,  Up: Top

Concept Index
*************

This is an alphabetical list of the files, tools, and concepts
introduced in this document.

[index]
* Menu:

* !:                                     Limitations of Builtins.
                                                              (line  16)
* "$@":                                  Shell Substitutions. (line  31)
* $(COMMANDS):                           Shell Substitutions. (line 132)
* ${VAR:-VALUE}:                         Shell Substitutions. (line  38)
* ${VAR=EXPANDED-VALUE}:                 Shell Substitutions. (line  71)
* ${VAR=LITERAL}:                        Shell Substitutions. (line  42)
* /usr/xpg4/bin/sh on Solaris:           Shellology.          (line  43)
* ::                                     Limitations of Builtins.
                                                              (line 312)
* @%:@:                                  Quadrigraphs.        (line   6)
* @:>@:                                  Quadrigraphs.        (line   6)
* @<:@:                                  Quadrigraphs.        (line   6)
* @S|@:                                  Quadrigraphs.        (line   6)
* 'COMMANDS':                            Shell Substitutions. (line 117)
* acconfig.h:                            acconfig.h.          (line   6)
* aclocal.m4:                            Making configure Scripts.
                                                              (line   6)
* Ash:                                   Shellology.          (line  13)
* autoconf:                              autoconf Invocation. (line   6)
* autoheader:                            autoheader Invocation.
                                                              (line   6)
* Automake:                              Automake.            (line  19)
* autoreconf:                            autoreconf Invocation.
                                                              (line   6)
* autoscan:                              autoscan Invocation. (line   6)
* autoupdate:                            autoupdate Invocation.
                                                              (line   6)
* awk:                                   Limitations of Usual Tools.
                                                              (line  10)
* Back trace:                            autoconf Invocation. (line  93)
* Bash:                                  Shellology.          (line  37)
* break:                                 Limitations of Builtins.
                                                              (line  19)
* Cache:                                 Caching Results.     (line   6)
* Cache variable:                        Cache Variable Names.
                                                              (line   6)
* Cache, enabling:                       configure Invocation.
                                                              (line  18)
* case:                                  Limitations of Builtins.
                                                              (line  22)
* cat:                                   Limitations of Usual Tools.
                                                              (line  53)
* cmp:                                   Limitations of Usual Tools.
                                                              (line  61)
* Command Substitution:                  Shell Substitutions. (line 117)
* config.h:                              Configuration Headers.
                                                              (line   6)
* config.h.bot:                          acconfig.h.          (line   6)
* config.h.in:                           Header Templates.    (line   6)
* config.h.top:                          acconfig.h.          (line   6)
* config.status:                         config.status Invocation.
                                                              (line   6)
* Configuration Header:                  Configuration Headers.
                                                              (line   6)
* Configuration Header Template:         Header Templates.    (line   6)
* configure:                             Making configure Scripts.
                                                              (line   6)
* configure <1>:                         Running configure scripts.
                                                              (line   6)
* configure.ac:                          Making configure Scripts.
                                                              (line  27)
* configure.in:                          Making configure Scripts.
                                                              (line  27)
* Copyright Notice:                      Notices.             (line  21)
* cp:                                    Limitations of Usual Tools.
                                                              (line  68)
* Declaration, checking:                 Declarations.        (line   6)
* diff:                                  Limitations of Usual Tools.
                                                              (line  79)
* dirname:                               Limitations of Usual Tools.
                                                              (line  85)
* dnl:                                   Macro Definitions.   (line  35)
* dnl <1>:                               Coding Style.        (line  40)
* echo:                                  Limitations of Builtins.
                                                              (line  42)
* egrep:                                 Limitations of Usual Tools.
                                                              (line 112)
* Endianness:                            C Compiler.          (line  68)
* exit:                                  Limitations of Builtins.
                                                              (line  69)
* export:                                Limitations of Builtins.
                                                              (line  94)
* expr:                                  Limitations of Usual Tools.
                                                              (line 126)
* expr <1>:                              Limitations of Usual Tools.
                                                              (line 151)
* expr (|):                              Limitations of Usual Tools.
                                                              (line 132)
* false:                                 Limitations of Builtins.
                                                              (line 120)
* File, checking:                        Files.               (line   6)
* for:                                   Limitations of Builtins.
                                                              (line 124)
* Function, checking:                    Particular Functions.
                                                              (line   6)
* grep:                                  Limitations of Usual Tools.
                                                              (line 204)
* Header, checking:                      Header Files.        (line   6)
* if:                                    Limitations of Builtins.
                                                              (line 146)
* ifnames:                               ifnames Invocation.  (line   6)
* Includes, default:                     Default Includes.    (line   6)
* Instantiation:                         Output.              (line  12)
* Language:                              Language Choice.     (line   6)
* Library, checking:                     Libraries.           (line   6)
* Libtool:                               Libtool.             (line  13)
* Links:                                 Configuration Links. (line  12)
* ln:                                    Limitations of Usual Tools.
                                                              (line 216)
* M4sugar:                               Programming in M4sugar.
                                                              (line   6)
* Macro invocation stack:                autoconf Invocation. (line  93)
* Messages, from autoconf:               Reporting Messages.  (line   6)
* Messages, from configure:              Printing Messages.   (line   6)
* mv:                                    Limitations of Usual Tools.
                                                              (line 228)
* obstack:                               Particular Functions.
                                                              (line 176)
* POSIX termios headers:                 System Services.     (line  62)
* Previous Variable:                     Setting Output Variables.
                                                              (line  44)
* Programs, checking:                    Alternative Programs.
                                                              (line   6)
* QNX 4.25:                              Systemology.         (line  11)
* quadrigraphs:                          Quadrigraphs.        (line   6)
* quotation:                             Autoconf Language.   (line   6)
* quotation <1>:                         M4 Quotation.        (line   6)
* Revision:                              Notices.             (line  29)
* sed:                                   Limitations of Usual Tools.
                                                              (line 239)
* sed (t):                               Limitations of Usual Tools.
                                                              (line 278)
* set:                                   Limitations of Builtins.
                                                              (line 175)
* shift:                                 Limitations of Builtins.
                                                              (line 186)
* Structure, checking:                   Structures.          (line   6)
* Symbolic links:                        Limitations of Usual Tools.
                                                              (line 216)
* termios POSIX headers:                 System Services.     (line  62)
* test:                                  Limitations of Builtins.
                                                              (line 191)
* touch:                                 Limitations of Usual Tools.
                                                              (line 338)
* trap:                                  Limitations of Builtins.
                                                              (line 272)
* true:                                  Limitations of Builtins.
                                                              (line 312)
* undefined macro: _m4_divert_diversion: New Macros.          (line   6)
* unset:                                 Limitations of Builtins.
                                                              (line 323)
* Variable, Precious:                    Setting Output Variables.
                                                              (line  44)
* Version:                               Notices.             (line  10)
* VPATH:                                 Limitations of Make. (line  31)
* Zsh:                                   Shellology.          (line  49)



Tag Table:
Node: Top1982
Node: Introduction14243
Ref: Introduction-Footnote-119088
Ref: Introduction-Footnote-219169
Ref: Introduction-Footnote-319269
Ref: Introduction-Footnote-419383
Node: The GNU build system19458
Node: Automake20377
Node: Libtool22803
Node: Pointers24229
Ref: Pointers-Footnote-125435
Ref: Pointers-Footnote-225494
Ref: Pointers-Footnote-325551
Ref: Pointers-Footnote-425693
Ref: Pointers-Footnote-525767
Ref: Pointers-Footnote-625839
Node: Making configure Scripts25914
Node: Writing configure.ac28948
Node: Shell Script Compiler30414
Node: Autoconf Language32715
Node: configure.ac Layout37347
Node: autoscan Invocation38751
Node: ifnames Invocation41504
Node: autoconf Invocation42704
Node: autoreconf Invocation49781
Node: Setup53123
Node: Notices54328
Node: Input55964
Node: Output58012
Node: Configuration Actions59994
Node: Configuration Files62899
Node: Makefile Substitutions64365
Node: Preset Output Variables66048
Node: Installation Directory Variables70619
Node: Build Directories74971
Node: Automatic Remaking76624
Node: Configuration Headers78779
Node: Header Templates81482
Node: autoheader Invocation82760
Node: Autoheader Macros86228
Node: Configuration Commands88431
Node: Configuration Links90117
Node: Subdirectories91489
Node: Default Prefix93644
Node: Existing Tests95041
Node: Common Behavior96759
Node: Standard Symbols97421
Node: Default Includes98022
Node: Alternative Programs99954
Node: Particular Programs100640
Node: Generic Programs106101
Node: Files110010
Node: Libraries110905
Node: Library Functions113770
Node: Function Portability114393
Node: Particular Functions115398
Node: Generic Functions125990
Node: Header Files130235
Node: Particular Headers130798
Node: Generic Headers137767
Node: Declarations139839
Node: Particular Declarations140428
Node: Generic Declarations140851
Node: Structures143224
Node: Particular Structures143831
Node: Generic Structures145553
Node: Types146797
Node: Particular Types147317
Node: Generic Types148487
Node: Compilers and Preprocessors149859
Node: Generic Compiler Characteristics150870
Node: C Compiler151733
Node: C++ Compiler159074
Node: Fortran 77 Compiler161317
Node: System Services169814
Ref: System Services-Footnote-1172930
Node: UNIX Variants173021
Node: Writing Tests174203
Node: Examining Declarations176135
Node: Examining Syntax178635
Node: Examining Libraries180083
Node: Run Time183095
Node: Test Programs184076
Node: Guidelines186343
Node: Test Functions187542
Node: Systemology189098
Ref: Systemology-Footnote-1189726
Ref: Systemology-Footnote-2189764
Node: Multiple Cases189832
Node: Language Choice191089
Node: Results193124
Node: Defining Symbols193874
Node: Setting Output Variables197130
Node: Caching Results201321
Node: Cache Variable Names205004
Node: Cache Files206593
Node: Cache Checkpointing208623
Node: Printing Messages209954
Node: Programming in M4213139
Node: M4 Quotation213812
Node: Active Characters214622
Ref: Active Characters-Footnote-1216000
Node: One Macro Call216022
Node: Quotation and Nested Macros217584
Node: Quadrigraphs220550
Node: Quotation Rule Of Thumb221475
Node: Programming in M4sugar224118
Node: Redefined M4 Macros224626
Node: Forbidden Patterns225596
Node: Writing Autoconf Macros226961
Node: Macro Definitions227762
Node: Macro Names229570
Node: Reporting Messages232171
Node: Dependencies Between Macros233517
Node: Prerequisite Macros234141
Node: Suggested Ordering236922
Node: Obsoleting Macros238441
Node: Coding Style239564
Node: Portable Shell246570
Node: Shellology248656
Node: Here-Documents251635
Node: File Descriptors253597
Node: File System Conventions255605
Ref: File System Conventions-Footnote-1259725
Node: Shell Substitutions259799
Node: Assignments264708
Node: Special Shell Variables266345
Node: Limitations of Builtins270391
Node: Limitations of Usual Tools282719
Node: Limitations of Make295462
Node: Manual Configuration296443
Node: Specifying Names297272
Ref: Specifying Names-Footnote-1300083
Node: Canonicalizing300483
Node: Using System Type302887
Node: Site Configuration303936
Node: External Software304769
Node: Package Options308085
Node: Pretty Help Strings310953
Node: Site Details312932
Node: Transforming Names314167
Node: Transformation Options315315
Node: Transformation Examples315819
Node: Transformation Rules317541
Node: Site Defaults319377
Node: Running configure scripts323296
Node: Basic Installation324313
Node: Compilers and Options327161
Node: Multiple Architectures327803
Node: Installation Names328802
Node: Optional Features330001
Node: System Type330785
Node: Sharing Defaults332311
Node: Environment Variables332953
Node: configure Invocation333639
Node: config.status Invocation334771
Node: Obsolete Constructs338596
Node: Obsolete config.status Use339522
Node: acconfig.h341321
Node: autoupdate Invocation343337
Node: Obsolete Macros345299
Node: Autoconf 1362452
Node: Changed File Names363518
Node: Changed Makefiles364293
Node: Changed Macros365386
Node: Changed Results366642
Node: Changed Macro Writing368753
Node: Autoconf 2.13370028
Node: Changed Quotation371037
Node: New Macros372944
Node: Questions374578
Node: Distributing375102
Node: Why GNU m4376173
Node: Bootstrapping377071
Node: Why Not Imake377687
Node: History382392
Node: Genesis383191
Node: Exodus384387
Node: Leviticus387438
Node: Numbers388972
Node: Deuteronomy390893
Node: Environment Variable Index393565
Node: Output Variable Index397608
Node: Preprocessor Symbol Index407637
Node: Autoconf Macro Index418644
Node: M4 Macro Index441976
Node: Concept Index442663

End Tag Table


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