STRERROR(3) Linux Programmer's Manual STRERROR(3)
NAME
strerror, strerror_r, strerror_l - return string describing error number
SYNOPSIS
#include <string.h>
char *strerror(int errnum);
int strerror_r(int errnum, char *buf, size_t buflen);
/* XSI-compliant */
char *strerror_r(int errnum, char *buf, size_t buflen);
/* GNU-specific */
char *strerror_l(int errnum, locale_t locale);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
strerror_r():
The XSI-compliant version is provided if:
(_POSIX_C_SOURCE >= 200112L) && ! _GNU_SOURCE
Otherwise, the GNU-specific version is provided.
DESCRIPTION
The strerror() function returns a pointer to a string that describes the error code passed in the argument errnum, possibly using the
LC_MESSAGES part of the current locale to select the appropriate language. (For example, if errnum is EINVAL, the returned description
will be "Invalid argument".) This string must not be modified by the application, but may be modified by a subsequent call to strerror()
or strerror_l(). No other library function, including perror(3), will modify this string.
strerror_r()
The strerror_r() function is similar to strerror(), but is thread safe. This function is available in two versions: an XSI-compliant ver-
sion specified in POSIX.1-2001 (available since glibc 2.3.4, but not POSIX-compliant until glibc 2.13), and a GNU-specific version (avail-
able since glibc 2.0). The XSI-compliant version is provided with the feature test macros settings shown in the SYNOPSIS; otherwise the
GNU-specific version is provided. If no feature test macros are explicitly defined, then (since glibc 2.4) _POSIX_C_SOURCE is defined by
default with the value 200112L, so that the XSI-compliant version of strerror_r() is provided by default.
The XSI-compliant strerror_r() is preferred for portable applications. It returns the error string in the user-supplied buffer buf of
length buflen.
The GNU-specific strerror_r() returns a pointer to a string containing the error message. This may be either a pointer to a string that
the function stores in buf, or a pointer to some (immutable) static string (in which case buf is unused). If the function stores a string
in buf, then at most buflen bytes are stored (the string may be truncated if buflen is too small and errnum is unknown). The string always
includes a terminating null byte ('