Using getopt for obtaining non-specified arguments C

Question

I'm writing a program which needs to be able to parse command line arguments, and I would like to use getopt. I have no issues with getting it to work with the regular arguments, however I need it to be able to pick up an argument that is not specified with a flag. For example if I ran: ./prog -a a1 -b b2 foo I would need to be able to get a1,a2 and foo. Right now it handles everything but the unspecified argument. Here is what I have:

while((command = getopt(argc, argv, "a:b:c:")) != -1){
        switch(command){
            case('a'):
                input = fopen(optarg, "r");
                if(input == NULL){
                    printf("Error opening file, exiting\n");
                    exit( -1 );
                }
                break;

            case('b'):
                output = fopen(optarg, "r");
                if(output == NULL){
                    printf("Error opening file, exiting\n");
                    exit( -1 );
                }
                break;

            case('c'):
                keyword = optarg;
                break;


            case('?'):
                if((optopt == 'a') || (optopt == 'b') || (optopt == 'c')){
                    fprintf(stderr, "Error, no argument specified for -%c\n", optopt);
                    exit( -1 );
                } else
                    extra = optarg; // This is how I thought I needed to do it

                break;

            default:
                fprintf(stderr,"Error in getopt");
                break;
        }// switch
    } // while

Thanks!

Answer 1

After the loop, the optind variable will be the index to the next non-option argument.

So do e.g.

if (optind < argc)
{
    printf("Have extra arguments: ");
    for (int i = optind; i < argc; ++i)
        printf("%s ", argv[i]);
    printf("\n");
}

to list all non-option arguments.