Using getopt in C for command line arguments

问题

I am working on trying to take in command line arguments. If I want to have multiple optional command line arguments how would I go about doing that? For example you can run the program in the following ways: (a is required every instance but -b -c -d can be given optionally and in any order)

./myprogram -a
./myprogram -a -c -d
./myprogram -a -d -b

I know that getopt()'s third argument is options. I can set these options to be "abc" but will the way I have my switch case set up causes the loop to break at each option.

回答1:

The order doesn't matter so far as getopt() is concerned. All that matters is your third argument to getopt() (ie: it's format string) is correct:

The follow format strings are all equivalent:

"c:ba"
"c:ab"
"ac:b"
"abc:"

In your particular case, the format string just needs to be something like "abcd", and the switch() statement is properly populated.

The following minimal example¹ will help.

#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 *cvalue = NULL;
  int index;
  int c;

  opterr = 0;

  while ((c = getopt (argc, argv, "abc:")) != -1)
  {
    switch (c)
      {
      case 'a':
        aflag = 1;
        break;
      case 'b':
        bflag = 1;
        break;
      case 'c':
        cvalue = optarg;
        break;
      case '?':
        if (optopt == 'c')
          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 ();
      }
  }

  printf ("aflag = %d, bflag = %d, cvalue = %s\n",
          aflag, bflag, cvalue);

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

¹Example taken from the GNU manual

来源：https://stackoverflow.com/questions/28129098/using-getopt-in-c-for-command-line-arguments