getopt.cpp

#include <string.h>
#include <stdio.h>

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    ("")

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

    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 != ':') {
            printf("illegal option -- %c\n", 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 == ':')
                return (BADARG);
            if (opterr)
                (void)printf("option requires an argument -- %c\n", optopt);
            return (BADCH);
        }
        else {                              /* white space */
            optarg = nargv[optind];
        }
        place = EMSG;
        ++optind;
    }
    return optopt;                          /* dump back option letter */
}