source: azure_iot_hub/trunk/musl-1.1.18/src/misc/getopt.c@ 389

#include <unistd.h>
#include <wchar.h>
#include <string.h>
#include <limits.h>
#include <stdlib.h>
#include "libc.h"
#include "locale_impl.h"

char *optarg;
int optind=1, opterr=1, optopt, __optpos, __optreset=0;

#define optpos __optpos
weak_alias(__optreset, optreset);

void __getopt_msg(const char *a, const char *b, const char *c, size_t l)
{
        FILE *f = stderr;
        b = __lctrans_cur(b);
        flockfile(f);
        fputs(a, f)>=0
        && fwrite(b, strlen(b), 1, f)
        && fwrite(c, 1, l, f)==l
        && putc('\n', f);
        funlockfile(f);
}

int getopt(int argc, char * const argv[], const char *optstring)
{
        int i;
        wchar_t c, d;
        int k, l;
        char *optchar;

        if (!optind || __optreset) {
                __optreset = 0;
                __optpos = 0;
                optind = 1;
        }

        if (optind >= argc || !argv[optind])
                return -1;

        if (argv[optind][0] != '-') {
                if (optstring[0] == '-') {
                        optarg = argv[optind++];
                        return 1;
                }
                return -1;
        }

        if (!argv[optind][1])
                return -1;

        if (argv[optind][1] == '-' && !argv[optind][2])
                return optind++, -1;

        if (!optpos) optpos++;
        if ((k = mbtowc(&c, argv[optind]+optpos, MB_LEN_MAX)) < 0) {
                k = 1;
                c = 0xfffd; /* replacement char */
        }
        optchar = argv[optind]+optpos;
        optpos += k;

        if (!argv[optind][optpos]) {
                optind++;
                optpos = 0;
        }

        if (optstring[0] == '-' || optstring[0] == '+')
                optstring++;

        i = 0;
        d = 0;
        do {
                l = mbtowc(&d, optstring+i, MB_LEN_MAX);
                if (l>0) i+=l; else i++;
        } while (l && d != c);

        if (d != c) {
                optopt = c;
                if (optstring[0] != ':' && opterr)
                        __getopt_msg(argv[0], ": unrecognized option: ", optchar, k);
                return '?';
        }
        if (optstring[i] == ':') {
                if (optstring[i+1] == ':') optarg = 0;
                else if (optind >= argc) {
                        optopt = c;
                        if (optstring[0] == ':') return ':';
                        if (opterr) __getopt_msg(argv[0],
                                ": option requires an argument: ",
                                optchar, k);
                        return '?';
                }
                if (optstring[i+1] != ':' || optpos) {
                        optarg = argv[optind++] + optpos;
                        optpos = 0;
                }
        }
        return c;
}

weak_alias(getopt, __posix_getopt);