int
       main(int argc, char *argv[])
       {
           int base;
           char *endptr, *str;
           unsigned long val;

           if (argc < 2) {
               fprintf(stderr, "Usage: %s str [base]\n", argv[0]);
               exit(EXIT_FAILURE);
           }

           str = argv[1];
           base = 10;

           errno = 0;    /* To distinguish success/failure after call */
           val = strtoul(str, &endptr, base);

           /* Check for various possible errors */

           if ((errno == ERANGE && (val == ULONG_MAX))   || (errno != 0 && val == 0)) {
               perror("strtoul");
               exit(EXIT_FAILURE);
           }

           if (!isdigit(str[0])) {
               fprintf(stderr,"- character were found\n");
               exit(EXIT_FAILURE);
           }

           if (endptr == str) {
               fprintf(stderr, "No digits were found\n");
               exit(EXIT_FAILURE);
           }

           /* If we got here, strtol() successfully parsed a number */

           printf("strtul() returned %lu\n", val);

           if (*endptr != '\0')        /* Not necessarily an error... */
               printf("Further characters after number: %s\n", endptr);

           exit(EXIT_SUCCESS);
       }