Returns: One plus the number of marked sub-expressions in the regular expression that was matched if *this represents the result of a successful match. Otherwise returns 0. [ Note: The state of a match_results object can be modified only by passing that object to regex_match or regex_search. Sections [re.alg.match] and [re.alg.search] specify the effects of those algorithms on their match_results arguments. — end note ]
Returns: The maximum number of sub_match elements that can be stored in *this.
Returns: size() == 0.