_strerror()             Save System Error Message

 #include   <string.h>                   Required for declarations only

 char       *_strerror(string);
 const char *string;                     User supplied message

    _strerror() allows custom error messages to be created.

       Returns:     If 'string' is NULL, a pointer to the most recently
                    generated system error message is returned.  The
                    string is terminated by a null character.

                    If 'string' is not NULL, _strerror() returns a
                    pointer to a string that contains the customized
                    error message (supplied as the argument to
                    _strerror()), a colon, a space, the last system error
                    message, and a new-line character.

         Notes:     For accurate results, call _strerror() immediately
                    after a routine returns to avoid 'errno' being
                    overwritten by subsequent routine calls.

                    Unlike perror(), _strerror() does not actually print
                    any messages.  The program is responsible for
                    printing the returned message, as shown in the
                    example below.

   -------------------------------- Example ---------------------------------

    This example tries to open a file and prints a customized error
    message and exits if unable to do so.

           #include <string.h>
           #include <stdio.h>             /* for printf*/
           #include <fcntl.h>             /* constants defined */
           #include <sys\stat.h>          /* constants defined */
           #include <io.h>                /* for open */

           int fh;

           main()
           {
               if ((fh = open("invoice.dat",O_RDWR)) == -1) {
                    printf(_strerror("ERROR OPENING INVOICE FILE"));
                    exit(1);
               }
           }