public int get_match_count ()
Retrieves the number of matched substrings (including substring 0, that is the whole matched text), so 1 is returned if the pattern has no substrings in it and 0 is returned if the match failed.
If the last match was obtained using the DFA algorithm, that is using match_all or match_all_full, the retrieved count is not that of the number of capturing parentheses but that of the number of matched substrings.
a MatchInfo structure
Number of matched substrings, or -1 if an error occurred