strerror(3) — Linux manual page


strerror(3)             Library Functions Manual             strerror(3)

NAME         top

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

LIBRARY         top

       Standard C library (libc, -lc)

SYNOPSIS         top

       #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

       strerrorname_np(), strerrordesc_np():

           The XSI-compliant version is provided if:
               (_POSIX_C_SOURCE >= 200112L) && ! _GNU_SOURCE
           Otherwise, the GNU-specific version is provided.

DESCRIPTION         top

       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_r() function is similar to strerror(), but is thread
       safe.  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() 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

RETURN VALUE         top

       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         top

       EINVAL The value of errnum is not a valid error number.

       ERANGE Insufficient storage was supplied to contain the error
              description string.

ATTRIBUTES         top

       For an explanation of the terms used in this section, see
       │ Interface          Attribute     Value                    │
       │ strerror()         │ Thread safety │ MT-Unsafe race:strerror  │
       │ strerrorname_np(), │ Thread safety │ MT-Safe                  │
       │ strerrordesc_np()  │               │                          │
       │ strerror_r(),      │ Thread safety │ MT-Safe                  │
       │ strerror_l()       │               │                          │

STANDARDS         top

              C11, POSIX.1-2008.



       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         top

              POSIX.1-2001, C89.


              glibc 2.6.  POSIX.1-2008.

              glibc 2.32.

NOTES         top

       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

SEE ALSO         top

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

Linux man-pages (unreleased)     (date)                      strerror(3)

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