rb_str_subpat(str, re, nth)
    VALUE str, re;
    int nth;
{
    if (rb_reg_search(re, str, 0, 0) >= 0) {
	return rb_reg_nth_match(nth, rb_backref_get());
    }
    return Qnil;
}
rb_str_subpat(str, re, nth)
    VALUE str, re;
    int nth;
{
    if (rb_reg_search(re, str, 0, 0) >= 0) {
	return rb_reg_nth_match(nth, rb_backref_get());
    }
    return Qnil;
}