Something

   for (;;) {
      int option = getopt (argc, argv, "D");
      if (option == EOF) break;
      switch (option) {
         case 'D': options.Dflag   = TRUE; break;
         default : eprintf ("%s: -%c: invalid option\n",
                            progname, optopt);
                   exitcode = EXIT_FAILURE;
      };
   };