.\" Copyright (c) 1993 by Thomas Koenig (ig25@rz.uni-karlsruhe.de)
.\"
.\" 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.
.\"
.\" Since the Linux kernel and libraries are constantly changing, this
.\" manual page may be incorrect or out-of-date.  The author(s) assume no
.\" responsibility for errors or omissions, or for damages resulting from
.\" the use of the information contained herein.  The author(s) may not
.\" have taken the same level of care in the production of this manual,
.\" which is licensed free of charge, as they might when working
.\" professionally.
.\"
.\" Formatted or processed versions of this manual, if unaccompanied by
.\" the source, must acknowledge the copyright and authors of this work.
.\" License.
.\" 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 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  2008-08-29 "GNU" "Linux Programmer's Manual"
.SH NAME
confstr \- get configuration dependent string variables
.SH SYNOPSIS
.nf
.B #include <unistd.h>
.sp
.BI "size_t confstr(int " "name" ", char *" buf ", size_t " len );
.fi
.sp
.in -4n
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.in
.sp
.BR getcwd ():
_POSIX_C_SOURCE\ >=\ 2 || _XOPEN_SOURCE || _POSIX_SOURCE
.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 len
is not zero,
.BR confstr ()
copies the value of the string to
.I buf
truncated to
.I len \- 1
characters if necessary, with a null byte (\(aq\\0\(aq) as terminator.
This can be detected by comparing the return value of
.BR confstr ()
against
.IR len .
.PP
If
.I len
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 len ,
which means that the value in
.I buf
is truncated.

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
If the value of
.I name
is invalid.
.SH "CONFORMING TO"
POSIX.1-2001.
.SH EXAMPLE
The following code fragment determines the path where to find
the POSIX.2 system utilities:
.br
.nf
.in +4n

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);
.in
.fi
.SH "SEE ALSO"
.BR sh (1),
.BR exec (3),
.BR system (3)
.SH COLOPHON
This page is part of release 3.22 of the Linux
.I man-pages
project.
A description of the project,
and information about reporting bugs,
can be found at
http://www.kernel.org/doc/man-pages/.
