re.cpp

int main(){
	std::string pattern = "^<([\\w|_]+)>\\s*::=\\s*(.*)";
	std::regex p(pattern);
	std::smatch piece;
	string r = "<iter_stmt>     ::= WHILE(<expression>) <stmt>";
	std::regex_match(r, piece, p);
	cout << piece.size() << endl;
	for (size_t i = 0; i < piece.size(); ++i) {
		std::ssub_match sub_match = piece[i];
		std::string piece = sub_match.str();
		std::cout << "  submatch " << i << ": " << piece << '\n';
	}
	return 0;
}