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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.   (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


       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).


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

       ERANGE Insufficient storage was supplied to contain the error description 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

       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-


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


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                                            2013-06-21                                STRERROR(3)