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NAME
strerror, strerrorname_np, strerrordesc_np, strerror_r, strerror_l - return string
describing error number
LIBRARY
Standard C library (libc, -lc)
SYNOPSIS
#include <string.h>
char *strerror(int errnum);
const char *strerrorname_np(int errnum);
const char *strerrordesc_np(int errnum);
int strerror_r(int errnum, char buf[.buflen], size_t buflen);
/* XSI-compliant */
char *strerror_r(int errnum, char buf[.buflen], size_t buflen);
/* GNU-specific */
char *strerror_l(int errnum, locale_t locale);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
strerrorname_np(), strerrordesc_np():
_GNU_SOURCE
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, and the returned pointer will be invalidated on a subsequent call to
strerror() or strerror_l(), or if the thread that obtained the string exits. No other
library function, including perror(3), will modify this string.
Like strerror(), the strerrordesc_np() function returns a pointer to a string that
describes the error code passed in the argument errnum, with the difference that the
returned string is not translated according to the current locale.
The strerrorname_np() function returns a pointer to a string containing the name of the
error code passed in the argument errnum. For example, given EPERM as an argument, this
function returns a pointer to the string "EPERM". Given 0 as an argument, this function
returns a pointer to the string "0".
strerror_r()
strerror_r() is like strerror(), but might use the supplied buffer buf instead of
allocating one internally. This function is available in two versions: an XSI-compliant
version specified in POSIX.1-2001 (available since glibc 2.3.4, but not POSIX-compliant
until glibc 2.13), and a GNU-specific version (available 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
('\0').
strerror_l()
strerror_l() is like strerror(), but maps errnum to a locale-dependent error message in
the locale specified by locale. The behavior of strerror_l() is undefined if locale is
the special locale object LC_GLOBAL_LOCALE or is not a valid locale object handle.
RETURN VALUE
The strerror(), strerror_l(), and the GNU-specific strerror_r() functions return the
appropriate error description string, or an "Unknown error nnn" message if the error
number is unknown.
On success, strerrorname_np() and strerrordesc_np() return the appropriate error
description string. If errnum is an invalid error number, these functions return NULL.
The XSI-compliant strerror_r() function returns 0 on success. On error, a (positive)
error number is returned (since glibc 2.13), or -1 is returned and errno is set to
indicate the error (before glibc 2.13).
POSIX.1-2001 and POSIX.1-2008 require that a successful call to strerror() or strerror_l()
shall leave errno unchanged, and note that, since no function return value is reserved to
indicate an error, an application that wishes to check for errors should initialize errno
to zero before the call, and then check errno after the call.
ERRORS
EINVAL The value of errnum is not a valid error number.
ERANGE Insufficient storage was supplied to contain the error description string.
ATTRIBUTES
For an explanation of the terms used in this section, see attributes(7).
┌───────────────────┬───────────────┬─────────────────────────────────────────────────────┐
│Interface │ Attribute │ Value │
├───────────────────┼───────────────┼─────────────────────────────────────────────────────┤
│strerror() │ Thread safety │ MT-Safe │
├───────────────────┼───────────────┼─────────────────────────────────────────────────────┤
│strerrorname_np(), │ Thread safety │ MT-Safe │
│strerrordesc_np() │ │ │
├───────────────────┼───────────────┼─────────────────────────────────────────────────────┤
│strerror_r(), │ Thread safety │ MT-Safe │
│strerror_l() │ │ │
└───────────────────┴───────────────┴─────────────────────────────────────────────────────┘
Before glibc 2.32, strerror() is not MT-Safe.
STANDARDS
strerror()
C11, POSIX.1-2008.
strerror_r()
strerror_l()
POSIX.1-2008.
strerrorname_np()
strerrordesc_np()
GNU.
POSIX.1-2001 permits strerror() to set errno if the call encounters an error, but does not
specify what value should be returned as the function result in the event of an error. On
some systems, strerror() returns NULL if the error number is unknown. On other systems,
strerror() returns a string something like "Error nnn occurred" and sets errno to EINVAL
if the error number is unknown. C99 and POSIX.1-2008 require the return value to be non-
NULL.
HISTORY
strerror()
POSIX.1-2001, C89.
strerror_r()
POSIX.1-2001.
strerror_l()
glibc 2.6. POSIX.1-2008.
strerrorname_np()
strerrordesc_np()
glibc 2.32.
NOTES
strerrorname_np() and strerrordesc_np() are thread-safe and async-signal-safe.
SEE ALSO
err(3), errno(3), error(3), perror(3), strsignal(3), locale(7), signal-safety(7)