Brand-newbie boost::spirit::qi question. MSVS2012, boost 1.54 I have a response from a serial device that provides with 0 or more "profiles" in a given character format. I want to capture the number of profile responses in the list (semantic action) as well as have the value into the final result (std::vector<std::string>). How do I properly express this? Given the input.... (in this case, there are zero profiles returned) *ARSS:0<CR><LF>OK<CR><LF> Expect a vector of strings containing "*ARSS" "0" "OK" This sub-rule fails to return... (Not failing to parse) boost::spirit::qi::rule<Iter, std::vector<std::string>(), boost::spirit::qi::locals<int, std::string>> service_search_list; service_search_list %= // %= operator is necessary for attribute propagation when using symantic attributes (anything in [ ]) string ("*ARSS") >> colon >> // Initial response +digit [qi::_a = qi::_1] >> crlf >> // Number of discovered devices - save in local qi::_a qi::omit [ok [qi::_b = qi::_1]] >> // Match but don't emit the "OK" here - save it for the end qi::repeat (qi::_a) // Repeat for each discovered device [ crlf >> ( qi::hold [profile1] | qi::hold [profile2] ... ) ] >> qi::attr(qi::_b); // Emit the "OK" here at the end of the list Using qi::int_[qi::_a = qi::_1] provides and empty string "" in the result and not "0". If I omit the numeric input from the result... qi::omit [qi::int_[qi::_a = qi::_1]] the parse will succeed but number of items in the response list is lost in the final result (omitted as requested). Any suggestion is appreciated, I'm stumped.