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       strerror, strerror_r - return string describing error number


       #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 language.  This string must not be modified by the application, but
       may be modified by a subsequent call to perror(3) or strerror().  No library function 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),  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 the string always includes a terminating null byte.


       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.

       The XSI-compliant strerror_r() function returns 0 on success; on error, -1 is returned and
       errno is set to indicate the error.


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

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


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

       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.


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


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                                            2009-03-30                                STRERROR(3)