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);

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".

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).

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)