Program arguments on the command line

.: Program arguments on the command line :.

Although you can make your own routines to read and process the command line used to invoke your
program, everything is more practical when using the C library functions, as in the case of getopt_long ().

The example code that follows is a simple program that processes its arguments and shows on screen.

 #include <stdio.h>
 #include <unistd.h>
 #include <stdlib.h>
 
 #define _GNU_SOURCE
 #include <getopt.h>
 
 int main(int argc, char *argv[]) {
 
  int opt;
  int verbose_flag=0;
 
  struct option longopts[] = {
  {"help", 0, NULL, 'h'},
  {"file", 1, NULL, 'f'},
  {"verbose",0,&verbose_flag,1},
  {0,0,0,0}};
 
     while((opt = getopt_long(argc, argv, ":hf:", longopts, NULL)) != -1) {
         switch(opt) {
         case 'h':
             printf("option: %c\n", opt);
    printf("%s [-h|--help] [--verbose] [-f|--file <file>] [args]\n",argv[0]);
             break;
         case 'f':
             printf("option %c filename: %s\n", opt, optarg);
             break;
         case ':':
             printf("option %c needs a value\n", optopt);
             break;
         case '?':
             printf("unknown option: %c\n", optopt);
             break;
         }
     }
 
  if (verbose_flag != 0)
   printf("Verbose mode ON!\n");
  
     for(; optind < argc; optind++) {
   printf("optind: %d < argc: %d\n", optind, argc);
         printf("argument: %s (argv[%d])\n", argv[optind], optind);
   printf("\n");
  }
  
  while (optind < argc) {
   printf("optind: %d < argc: %d\n", optind, argc);
         printf("argument: %s (argv[%d])\n", argv[optind], optind);
   printf("\n");
   optind++;
  }
 
  printf("Out of the loop.\nflag: %d\noptind: %d e argc: %d\n", verbose_flag, optind, argc);
 
     exit(0);
 }