STRERROR(3)		   Linux Programmer's Manual		   STRERROR(3)

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 lan‐
       guage.  (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 fea‐
       ture test macros settings shown in the SYNOPSIS; otherwise the GNU-spe‐
       cific  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 str‐
       error_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  str‐
       error()	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 descrip‐
	      tion 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	 func‐
       tion  result  in	 the  event  of an error.  On some systems, strerror()
       returns NULL if the error number is unknown.  On	 other	systems,  str‐
       error()	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 3.55 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)

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