#include <stdio.h>
#include <stdbool.h>
#include <unistd.h>

#include <getopt.h>

#define	OPTLIST		"d"

int main(int argc, char *argv[])
{
    int		opt;

    .....
    opterr	= 0;
    while((opt = getopt(argc, argv, OPTLIST)) != -1) {
	if(opt == 'd')
            dflag = !dflag;
        else
            argc = -1;
    }
    if(argc < 0) {
        fprintf(stderr, "Usage: %s [-d] [filename]\n", progname);  
        exit(EXIT_FAILURE);
    }
    while(optind < argc) {
        process( argv[optind] );
        ++optind;
    }
    .....
    return 0;
}