Manpages - strerror.3

strerror, strerrorname_np, strerrordesc_np, strerror_r, strerror_l - return string describing error number

  #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.

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.

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 *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 (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.

EINVAL

The value of errnum is not a valid error number.

ERANGE

Insufficient storage was supplied to contain the error description string.

The *strerror_l*() function first appeared in glibc 2.6.

The *strerrorname_np*() and *strerrordesc_np*() functions first appeared in glibc 2.32.

For an explanation of the terms used in this section, see *attributes*(7).

*strerror*() is specified by POSIX.1-2001, POSIX.1-2008, C89, and C99. *strerror_r*() is specified by POSIX.1-2001 and POSIX.1-2008.

*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.

The GNU C Library uses a buffer of 1024 characters for strerror*(). This buffer size therefore should be sufficient to avoid an *ERANGE error when calling *strerror_r*().

*strerrorname_np*() and *strerrordesc_np*() are thread-safe and async-signal-safe.

*err*(3), *errno*(3), *error*(3), *perror*(3), *strsignal*(3), *locale*(7)

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