c++ - Error reporting in Boost Spirit -

i have following error handler @ bottom of parser grammar:

qi::on_error<qi::fail>(     launch,     std::cerr << phoenix::val("paring error in ") << spirit::_4 << std::endl               << phoenix::construct<std::string>(spirit::_3, spirit::_2)               << std::endl     ); 

the problem parser's input isn't broken-up new lines beforehand, resulting error statement all lines in source code error point until end. there straightforward alternative

phoenix::construct<std::string>(spirit::_3, spirit::_2) 

to print 1 line error occurs on? phoenix semantics giving me trouble if try search '\n'.

we need create phoenix function can take spirit parameters.

// lazy function error reporting struct reporterror {   // result type must explicit phoenix   template<typename, typename, typename, typename>   struct result { typedef void type; };    // contract string surrounding new-line characters   template<typename iter>   void operator()(iter first_iter, iter last_iter,                   iter error_iter, const qi::info& what) const {     std::string first(first_iter, error_iter);     std::string last(error_iter, last_iter);     auto first_pos = first.rfind('\n');     auto last_pos = last.find('\n');     auto error_line = ((first_pos == std::string::npos) ? first                         : std::string(first, first_pos + 1))                       + std::string(last, 0, last_pos);     auto error_pos = (error_iter - first_iter) + 1;     if (first_pos != std::string::npos) {       error_pos -= (first_pos + 1);     }     std::cerr << "parsing error in " << << std::endl               << error_line << std::endl               << std::setw(error_pos) << '^'               << std::endl;   } };  const phoenix::function<reporterror> report_error = reporterror(); 

then invoke function in error handler.

qi::on_error<qi::fail>(     launch,     report_error(spirit::_1, spirit::_2, spirit::_3, spirit::_4)     );