confstr(3) — Linux manual page


CONFSTR(3)              Linux Programmer's Manual             CONFSTR(3)

NAME         top

       confstr - get configuration dependent string variables

SYNOPSIS         top

       #include <unistd.h>

       size_t confstr(int name, char *buf, size_t len);

   Feature Test Macro Requirements for glibc (see

           _POSIX_C_SOURCE >= 2 || _XOPEN_SOURCE

DESCRIPTION         top

       confstr() gets the value of configuration-dependent string

       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
              A string which identifies the POSIX implementation
              supplied by this C library (e.g., "NPTL 2.3.4" or

              A value for the PATH variable which indicates where all
              the POSIX.2 standard utilities can be found.

       If buf is not NULL and len is not zero, confstr() copies the
       value of the string to buf truncated to len - 1 bytes if
       necessary, with a null byte ('\0') as terminator.  This can be
       detected by comparing the return value of confstr() against len.

       If len is zero and buf is NULL, confstr() just returns the value
       as defined below.

RETURN VALUE         top

       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 len, 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.

ERRORS         top

       EINVAL The value of name is invalid.

ATTRIBUTES         top

       For an explanation of the terms used in this section, see

       │Interface                             Attribute     Value   │
       │confstr()                             │ Thread safety │ MT-Safe │

CONFORMING TO         top

       POSIX.1-2001, POSIX.1-2008.

EXAMPLES         top

       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)
           confstr(_CS_PATH, pathbuf, n);

SEE ALSO         top

       getconf(1), sh(1), exec(3), fpathconf(3), pathconf(3),
       sysconf(3), system(3)

COLOPHON         top

       This page is part of release 5.13 of the Linux man-pages project.
       A description of the project, information about reporting bugs,
       and the latest version of this page, can be found at

GNU                            2021-03-22                     CONFSTR(3)

Pages that refer to this page: fpathconf(3)gnu_get_libc_version(3)sysconf(3)posixoptions(7)standards(7)