CONFSTR(3) Linux Programmer's Manual CONFSTR(3)NAME
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
DESCRIPTIONconfstr() 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 sys‐
tem (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").
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
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
EINVAL 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 == NULL)
confstr(_CS_PATH, pathbuf, n);
SEE ALSOgetconf(1), sh(1), exec(3), fpathconf(3)sysconf(3)pathconf(3) sys‐
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GNU 2014-03-20 CONFSTR(3)