NAME

       strerror, strerror_r - return string describing error number

SYNOPSIS

       #include <string.h>

       char *strerror(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 */

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       The XSI-compliant version of strerror_r() is provided if:
       (_POSIX_C_SOURCE >= 200112L || _XOPEN_SOURCE >= 600) && ! _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 "Invalid argument".)  This
       string must not be modified by the application, but may be modified by a subsequent call  to  strerror().
       No library function, including perror(3), will modify this string.

       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_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').

RETURN VALUE

       The strerror() 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.

       POSIX.1-2001  and  POSIX.1-2008 require that a successful call to strerror() 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 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).

ERRORS

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

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

ATTRIBUTES

   Multithreading (see pthreads(7))
       The strerror() function is not thread-safe.

       The strerror_r() function is thread-safe.

CONFORMING TO

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

       The GNU-specific strerror_r() function is a nonstandard extension.

       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.

SEE ALSO

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

COLOPHON

       This page is part of release 3.54 of the Linux man-pages project.  A  description  of  the  project,  and
       information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.

                                                   2013-06-21                                        STRERROR(3)