Linux Programmer’s Manual
confstr − get configuration dependent string variables
size_t confstr(int name, char *buf , size_t len);
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"
A value for the PATH variable which indicates where all the POSIX.2 standard utilities can be
If buf is not NULL and len is not zero, confstr() copies the value of the string to buf truncated to len − 1
characters 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.
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 EIN-
If the value of name is invalid.
The following code fragment determines the path where to find the POSIX.2 system utilities:
n = confstr(_CS_PATH,NULL,(size_t) 0);
pathbuf = malloc(n);
if (pathbuf =