getopt 实现 from rpcap

int     opterr = 1,         /* if error message should be printed */
    optind = 1,         /* index into parent argv vector */
    optopt,         /* character checked for validity */
    optreset;           /* reset getopt */
char    *optarg;        /* argument associated with option */

#define BADCH   (int)'?'
#define BADARG  (int)':'
#define EMSG    ""

#ifdef WIN32
char *__progname = "rpcapd";
#endif

/*
 * getopt --
 *      Parse argc/argv argument vector.
 */
int
getopt(nargc, nargv, ostr)
    int nargc;
    char * const *nargv;
    const char *ostr;
{
// WIN32    extern char *__progname;
    static char *place = EMSG;          /* option letter processing */
    char *oli;                  /* option letter list index */
    int ret;

    if (optreset || !*place) {          /* update scanning pointer */
        optreset = 0;
        if (optind >= nargc || *(place = nargv[optind]) != '-') {
            place = EMSG;
            return (-1);
        }
        if (place[1] && *++place == '-') {      /* found "--" */
            ++optind;
            place = EMSG;
            return (-1);
        }
    }                       /* option letter okay? */
    if ((optopt = (int)*place++) == (int)':' ||
        !(oli = strchr(ostr, optopt))) {
        /*
         * if the user didn't specify '-' as an option,
         * assume it means -1.
         */
        if (optopt == (int)'-')
            return (-1);
        if (!*place)
            ++optind;
        if (opterr && *ostr != ':' && optopt != BADCH)
            (void)fprintf(stderr,
                "%s: illegal option -- %c\n", __progname, optopt);
        return (BADCH);
    }
    if (*++oli != ':') {            /* don't need argument */
        optarg = NULL;
        if (!*place)
            ++optind;
    }
    else {                  /* need an argument */
        if (*place)             /* no white space */
            optarg = place;
        else if (nargc <= ++optind) {   /* no arg */
            place = EMSG;
            if (*ostr == ':')
                ret = BADARG;
            else
                ret = BADCH;
            if (opterr)
                (void)fprintf(stderr,
                    "%s: option requires an argument -- %c\n",
                    __progname, optopt);
            return (ret);
        }
        else                /* white space */
            optarg = nargv[optind];
        place = EMSG;
        ++optind;
    }
    return (optopt);            /* dump back option letter */
}