Regex_match not returnning multiple values

Question

Following What does std::match_results::size return? I tried to get this simple string to match

    #include <regex>
    using namespace std;
    void main() {
    stringstream ss(
            "<tag1 abc = \"Test ABC\" def = \"Test DEF\">");                                                                 string         line;
        regex          re_open_tag("<([[:alnum:]]+)( \\w* = \\\"[\\w|\\s]*\\\")*>");
        while (getline(ss, line, '\n')) {
            for (auto i = sregex_iterator(begin(line), end(line), re_open_tag); i != sregex_iterator();
                 i++) {
                auto &match = *i;
                for (auto i = 0UL; i < match.size(); i++) printf("Match:%s\n", match[i].str().c_str());
            }
    }
}

It successfully matches the string as a whole but I get the following output

Match:<tag1 abc = "Test ABC" def = "Test DEF">
Match:tag1
Match: def = "Hello  world"

Where did abc=... go from the set of matches. The std::sub_matches number 3 which is 1 less than what I'd expect.