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diff --git a/man7/feature_test_macros.7 b/man7/feature_test_macros.7 deleted file mode 100644 index ee414dd..0000000 --- a/man7/feature_test_macros.7 +++ /dev/null @@ -1,937 +0,0 @@ -.\" This manpage is Copyright (C) 2006, Michael Kerrisk -.\" -.\" SPDX-License-Identifier: Linux-man-pages-copyleft -.\" -.TH feature_test_macros 7 2023-10-31 "Linux man-pages 6.7" -.SH NAME -feature_test_macros \- feature test macros -.SH DESCRIPTION -Feature test macros allow the programmer to control the definitions that -are exposed by system header files when a program is compiled. -.P -.B NOTE: -In order to be effective, a feature test macro -.IR "must be defined before including any header files" . -This can be done either in the compilation command -.RI ( "cc \-DMACRO=value" ) -or by defining the macro within the source code before -including any headers. -The requirement that the macro must be defined before including any -header file exists because header files may freely include one another. -Thus, for example, in the following lines, defining the -.B _GNU_SOURCE -macro may have no effect because the header -.I <abc.h> -itself includes -.I <xyz.h> -(POSIX explicitly allows this): -.P -.in +4n -.EX -#include <abc.h> -#define _GNU_SOURCE -#include <xyz.h> -.EE -.in -.P -Some feature test macros are useful for creating portable applications, -by preventing nonstandard definitions from being exposed. -Other macros can be used to expose nonstandard definitions that -are not exposed by default. -.P -The precise effects of each of the feature test macros described below -can be ascertained by inspecting the -.I <features.h> -header file. -.BR Note : -applications do -.I not -need to directly include -.IR <features.h> ; -indeed, doing so is actively discouraged. -See NOTES. -.SS Specification of feature test macro requirements in manual pages -When a function requires that a feature test macro is defined, -the manual page SYNOPSIS typically includes a note of the following form -(this example from the -.BR acct (2) -manual page): -.P -.RS -.B #include <unistd.h> -.P -.BI "int acct(const char *" filename ); -.P -.RS -4 -.EX -Feature Test Macro Requirements for glibc (see -.BR feature_test_macros (7)): -.EE -.RE -.P -.BR acct (): -_BSD_SOURCE || (_XOPEN_SOURCE && _XOPEN_SOURCE < 500) -.RE -.P -The -.B || -means that in order to obtain the declaration of -.BR acct (2) -from -.IR <unistd.h> , -.I either -of the following macro -definitions must be made before including any header files: -.P -.in +4n -.EX -#define _BSD_SOURCE -#define _XOPEN_SOURCE /* or any value < 500 */ -.EE -.in -.P -Alternatively, equivalent definitions can be included in the -compilation command: -.P -.in +4n -.EX -cc \-D_BSD_SOURCE -cc \-D_XOPEN_SOURCE # Or any value < 500 -.EE -.in -.P -Note that, as described below, -.BR "some feature test macros are defined by default" , -so that it may not always be necessary to -explicitly specify the feature test macro(s) shown in the -SYNOPSIS. -.P -In a few cases, manual pages use a shorthand for expressing the -feature test macro requirements (this example from -.BR readahead (2)): -.P -.RS +4 -.EX -.B #define _GNU_SOURCE -.B #define _FILE_OFFSET_BITS 64 -.B #include <fcntl.h> -.P -.BI "ssize_t readahead(int " fd ", off_t *" offset ", size_t " count ); -.EE -.RE -.P -This format is employed when the feature test macros ensure -that the proper function declarations are visible, -and the macros are not defined by default. -.SS Feature test macros understood by glibc -The paragraphs below explain how feature test macros are handled -in glibc 2.\fIx\fP, -.I x -> 0. -.P -First, though, a summary of a few details for the impatient: -.IP \[bu] 3 -The macros that you most likely need to use in modern source code are -.B _POSIX_C_SOURCE -(for definitions from various versions of POSIX.1), -.B _XOPEN_SOURCE -(for definitions from various versions of SUS), -.B _GNU_SOURCE -(for GNU and/or Linux specific stuff), and -.B _DEFAULT_SOURCE -(to get definitions that would normally be provided by default). -.IP \[bu] -Certain macros are defined with default values. -Thus, although one or more macros may be indicated as being -required in the SYNOPSIS of a man page, -it may not be necessary to define them explicitly. -Full details of the defaults are given later in this man page. -.IP \[bu] -Defining -.B _XOPEN_SOURCE -with a value of 600 or greater produces the same effects as defining -.B _POSIX_C_SOURCE -with a value of 200112L or greater. -Where one sees -.IP -.in +4n -.EX -_POSIX_C_SOURCE >= 200112L -.EE -.in -.IP -in the feature test macro requirements in the SYNOPSIS of a man page, -it is implicit that the following has the same effect: -.IP -.in +4n -.EX -_XOPEN_SOURCE >= 600 -.EE -.in -.IP \[bu] -Defining -.B _XOPEN_SOURCE -with a value of 700 or greater produces the same effects as defining -.B _POSIX_C_SOURCE -with a value of 200809L or greater. -Where one sees -.IP -.in +4n -.EX -_POSIX_C_SOURCE >= 200809L -.EE -.in -.IP -in the feature test macro requirements in the SYNOPSIS of a man page, -it is implicit that the following has the same effect: -.IP -.in +4n -.EX -_XOPEN_SOURCE >= 700 -.EE -.in -.\" The details in glibc 2.0 are simpler, but combining a -.\" a description of them with the details in later glibc versions -.\" would make for a complicated description. -.P -glibc understands the following feature test macros: -.TP -.B __STRICT_ANSI__ -ISO Standard C. -This macro is implicitly defined by -.BR gcc (1) -when invoked with, for example, the -.I \-std=c99 -or -.I \-ansi -flag. -.TP -.B _POSIX_C_SOURCE -Defining this macro causes header files to expose definitions as follows: -.RS -.IP \[bu] 3 -The value 1 exposes definitions conforming to POSIX.1-1990 and -ISO C (1990). -.IP \[bu] -The value 2 or greater additionally exposes -definitions for POSIX.2-1992. -.IP \[bu] -The value 199309L or greater additionally exposes -definitions for POSIX.1b (real-time extensions). -.\" 199506L functionality is available only since glibc 2.1 -.IP \[bu] -The value 199506L or greater additionally exposes -definitions for POSIX.1c (threads). -.IP \[bu] -(Since glibc 2.3.3) -The value 200112L or greater additionally exposes definitions corresponding -to the POSIX.1-2001 base specification (excluding the XSI extension). -This value also causes C95 (since glibc 2.12) and -C99 (since glibc 2.10) features to be exposed -(in other words, the equivalent of defining -.BR _ISOC99_SOURCE ). -.IP \[bu] -(Since glibc 2.10) -The value 200809L or greater additionally exposes definitions corresponding -to the POSIX.1-2008 base specification (excluding the XSI extension). -.RE -.TP -.B _POSIX_SOURCE -Defining this obsolete macro with any value is equivalent to defining -.B _POSIX_C_SOURCE -with the value 1. -.IP -Since this macro is obsolete, -its usage is generally not documented when discussing -feature test macro requirements in the man pages. -.TP -.B _XOPEN_SOURCE -Defining this macro causes header files to expose definitions as follows: -.RS -.IP \[bu] 3 -Defining with any value exposes -definitions conforming to POSIX.1, POSIX.2, and XPG4. -.IP \[bu] -The value 500 or greater additionally exposes -definitions for SUSv2 (UNIX 98). -.IP \[bu] -(Since glibc 2.2) The value 600 or greater additionally exposes -definitions for SUSv3 (UNIX 03; i.e., the POSIX.1-2001 base specification -plus the XSI extension) and C99 definitions. -.IP \[bu] -(Since glibc 2.10) The value 700 or greater additionally exposes -definitions for SUSv4 (i.e., the POSIX.1-2008 base specification -plus the XSI extension). -.RE -.IP -If -.B __STRICT_ANSI__ -is not defined, or -.B _XOPEN_SOURCE -is defined with a value greater than or equal to 500 -.I and -neither -.B _POSIX_SOURCE -nor -.B _POSIX_C_SOURCE -is explicitly defined, then -the following macros are implicitly defined: -.RS -.IP \[bu] 3 -.B _POSIX_SOURCE -is defined with the value 1. -.IP \[bu] -.B _POSIX_C_SOURCE -is defined, according to the value of -.BR _XOPEN_SOURCE : -.RS -.TP -.BR _XOPEN_SOURCE " < 500" -.B _POSIX_C_SOURCE -is defined with the value 2. -.TP -.RB "500 <= " _XOPEN_SOURCE " < 600" -.B _POSIX_C_SOURCE -is defined with the value 199506L. -.TP -.RB "600 <= " _XOPEN_SOURCE " < 700" -.B _POSIX_C_SOURCE -is defined with the value 200112L. -.TP -.RB "700 <= " _XOPEN_SOURCE " (since glibc 2.10)" -.B _POSIX_C_SOURCE -is defined with the value 200809L. -.RE -.RE -.IP -In addition, defining -.B _XOPEN_SOURCE -with a value of 500 or greater produces the same effects as defining -.BR _XOPEN_SOURCE_EXTENDED . -.TP -.B _XOPEN_SOURCE_EXTENDED -If this macro is defined, -.I and -.B _XOPEN_SOURCE -is defined, then expose definitions corresponding to the XPG4v2 -(SUSv1) UNIX extensions (UNIX 95). -Defining -.B _XOPEN_SOURCE -with a value of 500 or more also produces the same effect as defining -.BR _XOPEN_SOURCE_EXTENDED . -Use of -.B _XOPEN_SOURCE_EXTENDED -in new source code should be avoided. -.IP -Since defining -.B _XOPEN_SOURCE -with a value of 500 or more has the same effect as defining -.BR _XOPEN_SOURCE_EXTENDED , -the latter (obsolete) feature test macro is generally not described in the -SYNOPSIS in man pages. -.TP -.BR _ISOC99_SOURCE " (since glibc 2.1.3)" -Exposes declarations consistent with the ISO C99 standard. -.IP -Earlier glibc 2.1.x versions recognized an equivalent macro named -.B _ISOC9X_SOURCE -(because the C99 standard had not then been finalized). -Although the use of this macro is obsolete, glibc continues -to recognize it for backward compatibility. -.IP -Defining -.B _ISOC99_SOURCE -also exposes ISO C (1990) Amendment 1 ("C95") definitions. -(The primary change in C95 was support for international character sets.) -.IP -Invoking the C compiler with the option -.I \-std=c99 -produces the same effects as defining this macro. -.TP -.BR _ISOC11_SOURCE " (since glibc 2.16)" -Exposes declarations consistent with the ISO C11 standard. -Defining this macro also enables C99 and C95 features (like -.BR _ISOC99_SOURCE ). -.IP -Invoking the C compiler with the option -.I \-std=c11 -produces the same effects as defining this macro. -.TP -.B _LARGEFILE64_SOURCE -Expose definitions for the alternative API specified by the -LFS (Large File Summit) as a "transitional extension" to the -Single UNIX Specification. -(See -.UR http:\:/\:/opengroup.org\:/platform\:/lfs.html -.UE .) -The alternative API consists of a set of new objects -(i.e., functions and types) whose names are suffixed with "64" -(e.g., -.I off64_t -versus -.IR off_t , -.BR lseek64 () -versus -.BR lseek (), -etc.). -New programs should not employ this macro; instead -.I _FILE_OFFSET_BITS=64 -should be employed. -.TP -.B _LARGEFILE_SOURCE -This macro was historically used to expose certain functions (specifically -.BR fseeko (3) -and -.BR ftello (3)) -that address limitations of earlier APIs -.RB ( fseek (3) -and -.BR ftell (3)) -that use -.I long -for file offsets. -This macro is implicitly defined if -.B _XOPEN_SOURCE -is defined with a value greater than or equal to 500. -New programs should not employ this macro; -defining -.B _XOPEN_SOURCE -as just described or defining -.B _FILE_OFFSET_BITS -with the value 64 is the preferred mechanism to achieve the same result. -.TP -.B _FILE_OFFSET_BITS -Defining this macro with the value 64 -automatically converts references to 32-bit functions and data types -related to file I/O and filesystem operations into references to -their 64-bit counterparts. -This is useful for performing I/O on large files (> 2 Gigabytes) -on 32-bit systems. -It is also useful when calling functions like -.BR copy_file_range (2) -that were added more recently and that come only in 64-bit flavors. -(Defining this macro permits correctly written programs to use -large files with only a recompilation being required.) -.IP -64-bit systems naturally permit file sizes greater than 2 Gigabytes, -and on those systems this macro has no effect. -.TP -.B _TIME_BITS -Defining this macro with the value 64 -changes the width of -.BR time_t (3type) -to 64-bit which allows handling of timestamps beyond -2038. -It is closely related to -.B _FILE_OFFSET_BITS -and depending on implementation, may require it set. -This macro is available as of glibc 2.34. -.TP -.BR _BSD_SOURCE " (deprecated since glibc 2.20)" -Defining this macro with any value causes header files to expose -BSD-derived definitions. -.IP -In glibc versions up to and including 2.18, -defining this macro also causes BSD definitions to be preferred in -some situations where standards conflict, unless one or more of -.BR _SVID_SOURCE , -.BR _POSIX_SOURCE , -.BR _POSIX_C_SOURCE , -.BR _XOPEN_SOURCE , -.BR _XOPEN_SOURCE_EXTENDED , -or -.B _GNU_SOURCE -is defined, in which case BSD definitions are disfavored. -Since glibc 2.19, -.B _BSD_SOURCE -no longer causes BSD definitions to be preferred in case of conflicts. -.IP -Since glibc 2.20, this macro is deprecated. -.\" commit c941736c92fa3a319221f65f6755659b2a5e0a20 -.\" commit 498afc54dfee41d33ba519f496e96480badace8e -.\" commit acd7f096d79c181866d56d4aaf3b043e741f1e2c -It now has the same effect as defining -.BR _DEFAULT_SOURCE , -but generates a compile-time warning (unless -.B _DEFAULT_SOURCE -.\" commit ade40b10ff5fa59a318cf55b9d8414b758e8df78 -is also defined). -Use -.B _DEFAULT_SOURCE -instead. -To allow code that requires -.B _BSD_SOURCE -in glibc 2.19 and earlier and -.B _DEFAULT_SOURCE -in glibc 2.20 and later to compile without warnings, define -.I both -.B _BSD_SOURCE -and -.BR _DEFAULT_SOURCE . -.TP -.BR _SVID_SOURCE " (deprecated since glibc 2.20)" -Defining this macro with any value causes header files to expose -System V-derived definitions. -(SVID == System V Interface Definition; see -.BR standards (7).) -.IP -Since glibc 2.20, this macro is deprecated in the same fashion as -.BR _BSD_SOURCE . -.TP -.BR _DEFAULT_SOURCE " (since glibc 2.19)" -This macro can be defined to ensure that the "default" -definitions are provided even when the defaults would otherwise -be disabled, -as happens when individual macros are explicitly defined, -or the compiler is invoked in one of its "standard" modes (e.g., -.IR cc\~\-std=c99 ). -Defining -.B _DEFAULT_SOURCE -without defining other individual macros -or invoking the compiler in one of its "standard" modes has no effect. -.IP -The "default" definitions comprise those required by POSIX.1-2008 and ISO C99, -as well as various definitions originally derived from BSD and System V. -On glibc 2.19 and earlier, these defaults were approximately equivalent -to explicitly defining the following: -.IP -.in +4n -.EX -cc \-D_BSD_SOURCE \-D_SVID_SOURCE \-D_POSIX_C_SOURCE=200809 -.EE -.in -.TP -.BR _ATFILE_SOURCE " (since glibc 2.4)" -Defining this macro with any value causes header files to expose -declarations of a range of functions with the suffix "at"; -see -.BR openat (2). -Since glibc 2.10, this macro is also implicitly defined if -.B _POSIX_C_SOURCE -is defined with a value greater than or equal to 200809L. -.TP -.B _GNU_SOURCE -Defining this macro (with any value) implicitly defines -.BR _ATFILE_SOURCE , -.BR _LARGEFILE64_SOURCE , -.BR _ISOC99_SOURCE , -.BR _XOPEN_SOURCE_EXTENDED , -.BR _POSIX_SOURCE , -.B _POSIX_C_SOURCE -with the value 200809L -(200112L before glibc 2.10; -199506L before glibc 2.5; -199309L before glibc 2.1) -and -.B _XOPEN_SOURCE -with the value 700 -(600 before glibc 2.10; -500 before glibc 2.2). -In addition, various GNU-specific extensions are also exposed. -.IP -Since glibc 2.19, defining -.B _GNU_SOURCE -also has the effect of implicitly defining -.BR _DEFAULT_SOURCE . -Before glibc 2.20, defining -.B _GNU_SOURCE -also had the effect of implicitly defining -.B _BSD_SOURCE -and -.BR _SVID_SOURCE . -.TP -.B _REENTRANT -Historically, on various C libraries -it was necessary to define this macro in all -multithreaded code. -.\" Zack Weinberg -.\" There did once exist C libraries where it was necessary. The ones -.\" I remember were proprietary Unix vendor libcs from the mid-1990s -.\" You would get completely unlocked stdio without _REENTRANT. -(Some C libraries may still require this.) -In glibc, -this macro also exposed definitions of certain reentrant functions. -.IP -However, glibc has been thread-safe by default for many years; -since glibc 2.3, the only effect of defining -.B _REENTRANT -has been to enable one or two of the same declarations that -are also enabled by defining -.B _POSIX_C_SOURCE -with a value of 199606L or greater. -.IP -.B _REENTRANT -is now obsolete. -In glibc 2.25 and later, defining -.B _REENTRANT -is equivalent to defining -.B _POSIX_C_SOURCE -with the value 199606L. -If a higher POSIX conformance level is -selected by any other means (such as -.B _POSIX_C_SOURCE -itself, -.BR _XOPEN_SOURCE , -.BR _DEFAULT_SOURCE , -or -.BR _GNU_SOURCE ), -then defining -.B _REENTRANT -has no effect. -.IP -This macro is automatically defined if one compiles with -.IR cc\~\-pthread . -.TP -.B _THREAD_SAFE -Synonym for the (deprecated) -.BR _REENTRANT , -provided for compatibility with some other implementations. -.TP -.BR _FORTIFY_SOURCE " (since glibc 2.3.4)" -.\" For more detail, see: -.\" http://gcc.gnu.org/ml/gcc-patches/2004-09/msg02055.html -.\" [PATCH] Object size checking to prevent (some) buffer overflows -.\" * From: Jakub Jelinek <jakub at redhat dot com> -.\" * To: gcc-patches at gcc dot gnu dot org -.\" * Date: Tue, 21 Sep 2004 04:16:40 -0400 -Defining this macro causes some lightweight checks to be performed -to detect some buffer overflow errors when employing -various string and memory manipulation functions (for example, -.BR memcpy (3), -.BR memset (3), -.BR stpcpy (3), -.BR strcpy (3), -.BR strncpy (3), -.BR strcat (3), -.BR strncat (3), -.BR sprintf (3), -.BR snprintf (3), -.BR vsprintf (3), -.BR vsnprintf (3), -.BR gets (3), -and wide character variants thereof). -For some functions, argument consistency is checked; -for example, a check is made that -.BR open (2) -has been supplied with a -.I mode -argument when the specified flags include -.BR O_CREAT . -Not all problems are detected, just some common cases. -.\" Look for __USE_FORTIFY_LEVEL in the header files -.IP -If -.B _FORTIFY_SOURCE -is set to 1, with compiler optimization level 1 -.RI ( "gcc\ \-O1" ) -and above, checks that shouldn't change the behavior of -conforming programs are performed. -With -.B _FORTIFY_SOURCE -set to 2, some more checking is added, but -some conforming programs might fail. -.\" For example, given the following code -.\" int d; -.\" char buf[1000], buf[1000]; -.\" strcpy(fmt, "Hello world\n%n"); -.\" snprintf(buf, sizeof(buf), fmt, &d); -.\" -.\" Compiling with "gcc -D_FORTIFY_SOURCE=2 -O1" and then running will -.\" cause the following diagnostic at run time at the snprintf() call -.\" -.\" *** %n in writable segment detected *** -.\" Aborted (core dumped) -.\" -.IP -Some of the checks can be performed at compile time -(via macros logic implemented in header files), -and result in compiler warnings; -other checks take place at run time, -and result in a run-time error if the check fails. -.IP -With -.B _FORTIFY_SOURCE -set to 3, additional checking is added to intercept -some function calls used with an argument of variable size -where the compiler can deduce an upper bound for its value. -For example, a program where -.BR malloc (3)'s -size argument is variable -can now be fortified. -.IP -Use of this macro requires compiler support, available since -gcc 4.0 and clang 2.6. -Use of -.B _FORTIFY_SOURCE -set to 3 requires gcc 12.0 or later, or clang 9.0 or later, -in conjunction with glibc 2.33 or later. -.\" glibc is not an absolute requirement (gcc has libssp; NetBSD/newlib -.\" and Darwin each have their own implementation), but let's keep it -.\" simple. -.SS Default definitions, implicit definitions, and combining definitions -If no feature test macros are explicitly defined, -then the following feature test macros are defined by default: -.B _BSD_SOURCE -(in glibc 2.19 and earlier), -.B _SVID_SOURCE -(in glibc 2.19 and earlier), -.B _DEFAULT_SOURCE -(since glibc 2.19), -.BR _POSIX_SOURCE , -and -.BR _POSIX_C_SOURCE =200809L -(200112L before glibc 2.10; -199506L before glibc 2.4; -199309L before glibc 2.1). -.P -If any of -.BR __STRICT_ANSI__ , -.BR _ISOC99_SOURCE , -.B _ISOC11_SOURCE -(since glibc 2.18), -.BR _POSIX_SOURCE , -.BR _POSIX_C_SOURCE , -.BR _XOPEN_SOURCE , -.B _XOPEN_SOURCE_EXTENDED -(in glibc 2.11 and earlier), -.B _BSD_SOURCE -(in glibc 2.19 and earlier), -or -.B _SVID_SOURCE -(in glibc 2.19 and earlier) -is explicitly defined, then -.BR _BSD_SOURCE , -.BR _SVID_SOURCE , -and -.B _DEFAULT_SOURCE -are not defined by default. -.P -If -.B _POSIX_SOURCE -and -.B _POSIX_C_SOURCE -are not explicitly defined, -and either -.B __STRICT_ANSI__ -is not defined or -.B _XOPEN_SOURCE -is defined with a value of 500 or more, then -.IP \[bu] 3 -.B _POSIX_SOURCE -is defined with the value 1; and -.IP \[bu] -.B _POSIX_C_SOURCE -is defined with one of the following values: -.RS -.IP \[bu] 3 -2, -if -.B _XOPEN_SOURCE -is defined with a value less than 500; -.IP \[bu] -199506L, -if -.B _XOPEN_SOURCE -is defined with a value greater than or equal to 500 and less than 600; -or -.IP \[bu] -(since glibc 2.4) 200112L, -if -.B _XOPEN_SOURCE -is defined with a value greater than or equal to 600 and less than 700. -.IP \[bu] -(Since glibc 2.10) -200809L, -if -.B _XOPEN_SOURCE -is defined with a value greater than or equal to 700. -.IP \[bu] -Older versions of glibc do not know about the values -200112L and 200809L for -.BR _POSIX_C_SOURCE , -and the setting of this macro will depend on the glibc version. -.IP \[bu] -If -.B _XOPEN_SOURCE -is undefined, then the setting of -.B _POSIX_C_SOURCE -depends on the glibc version: -199506L, before glibc 2.4; -200112L, since glibc 2.4 to glibc 2.9; and -200809L, since glibc 2.10. -.RE -.P -Multiple macros can be defined; the results are additive. -.SH STANDARDS -POSIX.1 specifies -.BR _POSIX_C_SOURCE , -.BR _POSIX_SOURCE , -and -.BR _XOPEN_SOURCE . -.P -.B _FILE_OFFSET_BITS -is not specified by any standard, -but is employed on some other implementations. -.P -.BR _BSD_SOURCE , -.BR _SVID_SOURCE , -.BR _DEFAULT_SOURCE , -.BR _ATFILE_SOURCE , -.BR _GNU_SOURCE , -.BR _FORTIFY_SOURCE , -.BR _REENTRANT , -and -.B _THREAD_SAFE -are specific to glibc. -.SH HISTORY -.B _XOPEN_SOURCE_EXTENDED -was specified by XPG4v2 (aka SUSv1), but is not present in SUSv2 and later. -.SH NOTES -.I <features.h> -is a Linux/glibc-specific header file. -Other systems have an analogous file, but typically with a different name. -This header file is automatically included by other header files as -required: it is not necessary to explicitly include it in order to -employ feature test macros. -.P -According to which of the above feature test macros are defined, -.I <features.h> -internally defines various other macros that are checked by -other glibc header files. -These macros have names prefixed by two underscores (e.g., -.BR __USE_MISC ). -Programs should -.I never -define these macros directly: -instead, the appropriate feature test macro(s) from the -list above should be employed. -.SH EXAMPLES -The program below can be used to explore how the various -feature test macros are set depending on the glibc version -and what feature test macros are explicitly set. -The following shell session, on a system with glibc 2.10, -shows some examples of what we would see: -.P -.in +4n -.EX -$ \fBcc ftm.c\fP -$ \fB./a.out\fP -_POSIX_SOURCE defined -_POSIX_C_SOURCE defined: 200809L -_BSD_SOURCE defined -_SVID_SOURCE defined -_ATFILE_SOURCE defined -$ \fBcc \-D_XOPEN_SOURCE=500 ftm.c\fP -$ \fB./a.out\fP -_POSIX_SOURCE defined -_POSIX_C_SOURCE defined: 199506L -_XOPEN_SOURCE defined: 500 -$ \fBcc \-D_GNU_SOURCE ftm.c\fP -$ \fB./a.out\fP -_POSIX_SOURCE defined -_POSIX_C_SOURCE defined: 200809L -_ISOC99_SOURCE defined -_XOPEN_SOURCE defined: 700 -_XOPEN_SOURCE_EXTENDED defined -_LARGEFILE64_SOURCE defined -_BSD_SOURCE defined -_SVID_SOURCE defined -_ATFILE_SOURCE defined -_GNU_SOURCE defined -.EE -.in -.SS Program source -\& -.EX -/* ftm.c */ -\& -#include <stdint.h> -#include <stdio.h> -#include <unistd.h> -#include <stdlib.h> -\& -int -main(int argc, char *argv[]) -{ -#ifdef _POSIX_SOURCE - printf("_POSIX_SOURCE defined\en"); -#endif -\& -#ifdef _POSIX_C_SOURCE - printf("_POSIX_C_SOURCE defined: %jdL\en", - (intmax_t) _POSIX_C_SOURCE); -#endif -\& -#ifdef _ISOC99_SOURCE - printf("_ISOC99_SOURCE defined\en"); -#endif -\& -#ifdef _ISOC11_SOURCE - printf("_ISOC11_SOURCE defined\en"); -#endif -\& -#ifdef _XOPEN_SOURCE - printf("_XOPEN_SOURCE defined: %d\en", _XOPEN_SOURCE); -#endif -\& -#ifdef _XOPEN_SOURCE_EXTENDED - printf("_XOPEN_SOURCE_EXTENDED defined\en"); -#endif -\& -#ifdef _LARGEFILE64_SOURCE - printf("_LARGEFILE64_SOURCE defined\en"); -#endif -\& -#ifdef _FILE_OFFSET_BITS - printf("_FILE_OFFSET_BITS defined: %d\en", _FILE_OFFSET_BITS); -#endif -\& -#ifdef _TIME_BITS - printf("_TIME_BITS defined: %d\en", _TIME_BITS); -#endif -\& -#ifdef _BSD_SOURCE - printf("_BSD_SOURCE defined\en"); -#endif -\& -#ifdef _SVID_SOURCE - printf("_SVID_SOURCE defined\en"); -#endif -\& -#ifdef _DEFAULT_SOURCE - printf("_DEFAULT_SOURCE defined\en"); -#endif -\& -#ifdef _ATFILE_SOURCE - printf("_ATFILE_SOURCE defined\en"); -#endif -\& -#ifdef _GNU_SOURCE - printf("_GNU_SOURCE defined\en"); -#endif -\& -#ifdef _REENTRANT - printf("_REENTRANT defined\en"); -#endif -\& -#ifdef _THREAD_SAFE - printf("_THREAD_SAFE defined\en"); -#endif -\& -#ifdef _FORTIFY_SOURCE - printf("_FORTIFY_SOURCE defined\en"); -#endif -\& - exit(EXIT_SUCCESS); -} -.EE -.SH SEE ALSO -.BR libc (7), -.BR standards (7), -.BR system_data_types (7) -.P -The section "Feature Test Macros" under -.IR "info libc" . -.\" But beware: the info libc document is out of date (Jul 07, mtk) -.P -.I /usr/include/features.h |