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NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | ATTRIBUTES | STANDARDS | HISTORY | EXAMPLES | SEE ALSO | COLOPHON |
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confstr(3) Library Functions Manual confstr(3)
confstr - get configuration dependent string variables
Standard C library (libc, -lc)
#include <unistd.h>
size_t confstr(size_t size;
int name, char buf[size], size_t size);
Feature Test Macro Requirements for glibc (see
feature_test_macros(7)):
confstr():
_POSIX_C_SOURCE >= 2 || _XOPEN_SOURCE
confstr() gets the value of configuration-dependent string
variables.
The name argument is the system variable to be queried. The
following variables are supported:
_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").
_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").
_CS_PATH
A value for the PATH variable which indicates where all the
POSIX.2 standard utilities can be found.
If buf is not NULL and size is not zero, confstr() copies the
value of the string to buf truncated to size - 1 bytes if
necessary, with a null byte ('\0') as terminator. This can be
detected by comparing the return value of confstr() against size.
If size is zero and buf is NULL, confstr() just returns the value
as defined below.
If name is a valid configuration variable, 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 size, which means that the value in buf is
truncated.
If name is a valid configuration variable, but that variable does
not have a value, then confstr() returns 0. If name does not
correspond to a valid configuration variable, confstr() returns 0,
and errno is set to EINVAL.
EINVAL The value of name is invalid.
For an explanation of the terms used in this section, see
attributes(7).
┌──────────────────────────────────────┬───────────────┬─────────┐
│ Interface │ Attribute │ Value │
├──────────────────────────────────────┼───────────────┼─────────┤
│ confstr() │ Thread safety │ MT-Safe │
└──────────────────────────────────────┴───────────────┴─────────┘
POSIX.1-2008.
POSIX.1-2001.
The following code fragment determines the path where to find the
POSIX.2 system utilities:
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);
getconf(1), sh(1), exec(3), fpathconf(3), pathconf(3), sysconf(3),
system(3)
This page is part of the man-pages (Linux kernel and C library
user-space interface documentation) project. Information about
the project can be found at
⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report
for this manual page, see
⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
This page was obtained from the tarball man-pages-6.15.tar.gz
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⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on
2025-08-11. If you discover any rendering problems in this HTML
version of the page, or you believe there is a better or more up-
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part of the original manual page), send a mail to
[email protected]
Linux man-pages 6.15 2025-06-28 confstr(3)
Pages that refer to this page: fpathconf(3), gnu_get_libc_version(3), sysconf(3), posixoptions(7), standards(7)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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