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'\" t
.\" Copyright (c) 1993 by Thomas Koenig (ig25@rz.uni-karlsruhe.de)
.\"
.\" SPDX-License-Identifier: Linux-man-pages-copyleft
.\"
.\" Modified Sat Jul 24 19:53:02 1993 by Rik Faith (faith@cs.unc.edu)
.\"
.\" FIXME Many more values for 'name' are supported, some of which
.\" are documented under 'info libc confstr'.
.\" See <bits/confname.h> for the rest.
.\" These should all be added to this page.
.\" See also the POSIX.1-2001 specification of confstr()
.\"
.TH confstr 3 2023-03-30 "Linux man-pages 6.04"
.SH NAME
confstr \- get configuration dependent string variables
.SH LIBRARY
Standard C library
.RI ( libc ", " \-lc )
.SH SYNOPSIS
.nf
.B #include <unistd.h>
.PP
.BI "size_t confstr(int " "name" ", char " buf [. size "], size_t " size );
.fi
.PP
.RS -4
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.RE
.PP
.BR confstr ():
.nf
_POSIX_C_SOURCE >= 2 || _XOPEN_SOURCE
.fi
.SH DESCRIPTION
.BR confstr ()
gets the value of configuration-dependent string variables.
.PP
The
.I name
argument is the system variable to be queried.
The following variables are supported:
.TP
.BR _CS_GNU_LIBC_VERSION " (GNU C library only; since glibc 2.3.2)"
A string which identifies the GNU C library version on this system
(e.g., "glibc 2.3.4").
.TP
.BR _CS_GNU_LIBPTHREAD_VERSION " (GNU C library only; since glibc 2.3.2)"
A string which identifies the POSIX implementation supplied by this
C library (e.g., "NPTL 2.3.4" or "linuxthreads\-0.10").
.TP
.B _CS_PATH
A value for the
.B PATH
variable which indicates where all the POSIX.2 standard utilities can
be found.
.PP
If
.I buf
is not NULL and
.I size
is not zero,
.BR confstr ()
copies the value of the string to
.I buf
truncated to
.I size \- 1
bytes if necessary, with a null byte (\[aq]\e0\[aq]) as terminator.
This can be detected by comparing the return value of
.BR confstr ()
against
.IR size .
.PP
If
.I size
is zero and
.I buf
is NULL,
.BR confstr ()
just returns the value as defined below.
.SH RETURN VALUE
If
.I name
is a valid configuration variable,
.BR confstr ()
returns the number of bytes (including the terminating null byte)
that would be required to hold the entire value of that variable.
This value may be greater than
.IR size ,
which means that the value in
.I buf
is truncated.
.PP
If
.I name
is a valid configuration variable,
but that variable does not have a value, then
.BR confstr ()
returns 0.
If
.I name
does not correspond to a valid configuration variable,
.BR confstr ()
returns 0, and
.I errno
is set to
.BR EINVAL .
.SH ERRORS
.TP
.B EINVAL
The value of
.I name
is invalid.
.SH ATTRIBUTES
For an explanation of the terms used in this section, see
.BR attributes (7).
.ad l
.nh
.TS
allbox;
lbx lb lb
l l l.
Interface Attribute Value
T{
.BR confstr ()
T} Thread safety MT-Safe
.TE
.hy
.ad
.sp 1
.SH STANDARDS
POSIX.1-2008.
.SH HISTORY
POSIX.1-2001.
.SH EXAMPLES
The following code fragment determines the path where to find
the POSIX.2 system utilities:
.PP
.in +4n
.EX
char *pathbuf;
size_t n;
n = confstr(_CS_PATH, NULL, (size_t) 0);
pathbuf = malloc(n);
if (pathbuf == NULL)
abort();
confstr(_CS_PATH, pathbuf, n);
.EE
.in
.SH SEE ALSO
.BR getconf (1),
.BR sh (1),
.BR exec (3),
.BR fpathconf (3),
.BR pathconf (3),
.BR sysconf (3),
.BR system (3)
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