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       strerror, strerror_r - return string describing error number


       #include <string.h>

       char *strerror(int errnum);

       char *strerror_r(int errnum, char *buf, size_t buflen);

   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


       The  strerror()  function  returns  a  string describing 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

       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


       The strerror() and 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 POSIX.1-2001.

       The GNU-specific strerror_r() function is a non-standard 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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                                  2007-07-26                       STRERROR(3)