Optopt and getopt in C

Question

I'm trying to figure out getopt, but I keep getting hung up at the end of the switch statement.

#include <ctype.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

int
main (int argc, char **argv)
{
  int aflag = 0;
  int bflag = 0;
  char *filename = NULL, *x = NULL;
  int index;
  int c;

  opterr = 0;
  while ((c = getopt (argc, argv, "hnc:")) != -1)
    switch (c)
      {
      case 'h':
        printf("You chose h");
        break;
      case 'n':
        x = optarg;
        break;
      case 'l':
        filename = optarg;
        break;
     case '?':
        if (optopt == 'n' || optopt == 'l')
          fprintf (stderr, "Option -%c requires an argument.\n", optopt);
        else if (isprint (optopt))
          fprintf (stderr, "Unknown option `-%c'.\n", optopt);
        else
          fprintf (stderr,
                   "Unknown option character `\\x%x'.\n",
                   optopt);
        return 1;
      default:
        abort ();
      }

  for (index = optind; index < argc; index++)
    printf ("Non-option argument %s\n", argv[index]);
  return 0;
}

When I compile this and run a.out -l it does as it should, but when I do a.out -n it does nothing, when it should say "Option n requires an argument."

How can I fix this?

Answer 1

Your optstring "hnc:" says n is a valid argument that doesn't require an argument, while l is not specified at all so the ? case will always be hit. Try using

getopt (argc, argv, "hn:l:")

which says n and l both require arguments.