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#### 25.2.4 Example of Parsing Long Options with `getopt_long`

         #include <stdio.h>
         #include <stdlib.h>
         #include <getopt.h>

         /* Flag set by ‘--verbose’. */
         static int verbose_flag;

         int
         main (int argc, char **argv)
         {
           int c;

           while (1)
             {
               static struct option long_options[] =
                 {
                   /* These options set a flag. */
                   {"verbose", no_argument,       &verbose_flag, 1},
                   {"brief",   no_argument,       &verbose_flag, 0},
                   /* These options don't set a flag.
                      We distinguish them by their indices. */
                   {"add",     no_argument,       0, 'a'},
                   {"append",  no_argument,       0, 'b'},
                   {"delete",  required_argument, 0, 'd'},
                   {"create",  required_argument, 0, 'c'},
                   {"file",    required_argument, 0, 'f'},
                   {0, 0, 0, 0}
                 };
               /* getopt_long stores the option index here. */
               int option_index = 0;

               c = getopt_long (argc, argv, "abc:d:f:",
                                long_options, &option_index);

               /* Detect the end of the options. */
               if (c == -1)
                 break;

               switch (c)
                 {
                 case 0:
                   /* If this option set a flag, do nothing else now. */
                   if (long_options[option_index].flag != 0)
                     break;
                   printf ("option %s", long_options[option_index].name);
                   if (optarg)
                     printf (" with arg %s", optarg);
                   printf ("\n");
                   break;

                 case 'a':
                   puts ("option -a\n");
                   break;

                 case 'b':
                   puts ("option -b\n");
                   break;

                 case 'c':
                   printf ("option -c with value `%s'\n", optarg);
                   break;

                 case 'd':
                   printf ("option -d with value `%s'\n", optarg);
                   break;

                 case 'f':
                   printf ("option -f with value `%s'\n", optarg);
                   break;

                 case '?':
                   /* getopt_long already printed an error message. */
                   break;

                 default:
                   abort ();
                 }
             }

           /* Instead of reporting ‘--verbose’
              and ‘--brief’ as they are encountered,
              we report the final status resulting from them. */
           if (verbose_flag)
             puts ("verbose flag is set");

           /* Print any remaining command line arguments (not options). */
           if (optind < argc)
             {
               printf ("non-option ARGV-elements: ");
               while (optind < argc)
                 printf ("%s ", argv[optind++]);
               putchar ('\n');
             }

           exit (0);
         }