#include <unistd.h>
int getopt(int argc, char * const argv[], const char *optstring);
extern char *optarg;
extern int optind, opterr, optopt;

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

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

    nsecs = 0;
    flags = 0;
    printf("first of all optind is %d\n", optind);
    printf("---at the begining,list argv value---\n");
    for (i=0; i<argc; i++){
        printf("argv[%u] is %s\n",i,argv[i]);
    }
    printf("-----------------------------\n");
    while ((opt = getopt(argc, argv, "nt:")) != -1) {
        printf("current optind is %d\n", optind);
        switch (opt) {
            case 'n':
                flags++;
                break;
            case 't':
                nsecs = atoi(optarg);
                flags++;
                break;
            default: /* '?' */
                fprintf(stderr, "Usage: %s [-t nsecs] [-n] name\n",argv[0]);
                exit(EXIT_FAILURE);
        }
    }

    printf("---at the end,list argv value---\n");
    for (i=0; i<argc; i++){
        printf("argv[%u] is %s\n",i,argv[i]);
    }
    printf("-----------------------------\n");
    printf("after all optind is %d\n", optind);

    printf("flags=%d; nsecs=%d\n", flags, nsecs);

    if (optind >= argc) {
        fprintf(stderr, "Expected argument after options\n");
        exit(EXIT_FAILURE);
    }
    printf("name argument = %s\n", argv[optind]);

    /* Other code omitted */

    exit(EXIT_SUCCESS);
}