boost_spirit_cpp_lambda.cpp

#include<boost/spirit/include/qi.hpp>
#include<iostream>
#include<complex>
#include<string>

template <typename Iterator>
bool parse_complex(Iterator first, Iterator last, std::complex<double>& c){
    namespace qi = boost::spirit::qi;
    namespace ascii = boost::spirit::ascii;
    using qi::double_;
    using qi::phrase_parse;
    using ascii::space;

    double rN = 0.0;
    double iN = 0.0;
    auto cap_real = [&](double x){rN = x; };
    auto cap_img = [&](double x){iN = x; };
    bool r = phrase_parse(first, last,
			  (
			   '(' 
			   >> double_[cap_real]
			   >> -( ',' >> double_[cap_img]) 
			   >> ')'
			   | double_[cap_real]
			   ),
			  space);

    if (!r || first != last)
	return false;
    c = std::complex<double>(rN, iN);
    return r;
}

int main(){
    std::string str("(0.42, 2.5)");


    std::complex<double> c;
    parse_complex(str.begin(), str.end(), c);
    std::cout << c << std::endl;
}