#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.

       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

       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').

       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.

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

       ERANGE Insufficient  storage was supplied to contain the error descrip-
              tion string.

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

       The strerror_r() function is thread-safe.

       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.

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

       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

                                  2013-06-21                       STRERROR(3)
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