#include <stdlib.h>
#include <string.h>

int getsubopt(char** opt, char* const* keys, char** val) {
    char* s = *opt;
    int i;

    *val = NULL;
    *opt = strchr(s, ',');
    if (*opt)
        *(*opt)++ = 0;
    else
        *opt = s + strlen(s);

    for (i = 0; keys[i]; i++) {
        size_t l = strlen(keys[i]);
        if (strncmp(keys[i], s, l))
            continue;
        if (s[l] == '=')
            *val = s + l + 1;
        else if (s[l])
            continue;
        return i;
    }
    return -1;
}