skip_prefix
p += skip_prefix(p, &prf);
p += skip_prefix(p, &prf);
p += skip_prefix(p, &prf);
p += skip_prefix(p, &prf);
p += skip_prefix(p, &prf);
rest = skip_prefix(arg, options->long_name);
rest = skip_prefix(arg, options->long_name + 3);
rest = skip_prefix(arg + 3, options->long_name);