#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, 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)):
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.
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".
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').
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 (glibc versions before 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.
The strerrorname_np() and strerrordesc_np() functions first appeared in glibc 2.32.
| Interface | Attribute | Value |
| strerror() | Thread safety |
MT-Unsafe race:strerror
|
| strerrorname_np(), strerrordesc_np() | Thread safety | MT-Safe |
| strerror_r(), strerror_l() | Thread safety | MT-Safe |
strerror_l() is specified in POSIX.1-2008.
The GNU-specific functions strerror_r(), strerrorname_np(), and strerrordesc_np() are nonstandard extensions.
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.
strerrorname_np() and strerrordesc_np() are thread-safe and async-signal-safe.