Can not specify a skipper in boost spirit (compiler error)

Question

I am trying to build a parser using boost::spirit that, besides other stuff, should be able to parse pairs of integers such as "(3,4)".

My code is working but I also want to accept pairs that contain spaces, i.e. "( 4 , 6 )". When trying to add the space_type skipper as shown in the boost spirit tutorial the following code fails to compile. I can not see the grave mistake I am making (I suspected using the wrong namespace but it seems to be the correct one).

#include <boost/config/warning_disable.hpp>
#include <boost/spirit/include/qi.hpp>
#include <boost/spirit/include/phoenix.hpp>
#include <boost/fusion/include/std_pair.hpp>

using namespace std;
using namespace boost::spirit::qi;

using position = std::pair<int,  int>;

template<typename Iterator>
struct position_grammar : grammar<Iterator, position(), boost::spirit::ascii::space_type> {
    position_grammar() : position_grammar::base_type(start) {
        start = lit("(") >> int_ >> lit(",") >> int_ >> lit(")");
    }
    rule<Iterator, position(),boost::spirit::ascii::space_type> start;
};

int main() {
    std::string s = "(1,2)";
    position_grammar<std::string::iterator> grammar;
    position p;
    bool r = parse(s.begin(), s.end(), grammar,p);
    cout << "parsing: " << r << " position: " << p.first << ", " << p.second << "\n";
    return 0;
}

Compiler output:

In file included from /usr/include/boost/spirit/home/qi/nonterminal.hpp:14:0,
                 from /usr/include/boost/spirit/home/qi.hpp:21,
                 from /usr/include/boost/spirit/include/qi.hpp:16,
                 from /home/pansen/proggs/foo/src/foo/model/routing_parser_test.cpp:2:
/usr/include/boost/spirit/home/qi/nonterminal/rule.hpp: In instantiation of ‘bool boost::spirit::qi::rule<Iterator, T1, T2, T3, T4>::parse(Iterator&, const Iterator&, Context&, const Skipper&, Attribute&) const [with Context = boost::spirit::context<boost::fusion::cons<std::pair<int, int>&, boost::fusion::nil_>, boost::spirit::locals<> >; Skipper = boost::spirit::unused_type; Attribute = std::pair<int, int>; Iterator = __gnu_cxx::__normal_iterator<char*, std::__cxx11::basic_string<char> >; T1 = std::pair<int, int>(); T2 = boost::proto::exprns_::expr<boost::proto::tagns_::tag::terminal, boost::proto::argsns_::term<boost::spirit::tag::char_code<boost::spirit::tag::space, boost::spirit::char_encoding::ascii> >, 0l>; T3 = boost::spirit::unused_type; T4 = boost::spirit::unused_type]’:
/usr/include/boost/spirit/home/qi/reference.hpp:43:72:   required from ‘bool boost::spirit::qi::reference<Subject>::parse(Iterator&, const Iterator&, Context&, const Skipper&, Attribute&) const [with Iterator = __gnu_cxx::__normal_iterator<char*, std::__cxx11::basic_string<char> >; Context = boost::spirit::context<boost::fusion::cons<std::pair<int, int>&, boost::fusion::nil_>, boost::spirit::locals<> >; Skipper = boost::spirit::unused_type; Attribute = std::pair<int, int>; Subject = const boost::spirit::qi::rule<__gnu_cxx::__normal_iterator<char*, std::__cxx11::basic_string<char> >, std::pair<int, int>(), boost::proto::exprns_::expr<boost::proto::tagns_::tag::terminal, boost::proto::argsns_::term<boost::spirit::tag::char_code<boost::spirit::tag::space, boost::spirit::char_encoding::ascii> >, 0l>, boost::spirit::unused_type, boost::spirit::unused_type>]’
/usr/include/boost/spirit/home/qi/parse.hpp:86:82:   required from ‘bool boost::spirit::qi::parse(Iterator&, Iterator, const Expr&, Attr&) [with Iterator = __gnu_cxx::__normal_iterator<char*, std::__cxx11::basic_string<char> >; Expr = position_grammar<__gnu_cxx::__normal_iterator<char*, std::__cxx11::basic_string<char> > >; Attr = std::pair<int, int>]’
/usr/include/boost/spirit/home/qi/parse.hpp:98:25:   required from ‘bool boost::spirit::qi::parse(const Iterator&, Iterator, const Expr&, Attr&) [with Iterator = __gnu_cxx::__normal_iterator<char*, std::__cxx11::basic_string<char> >; Expr = position_grammar<__gnu_cxx::__normal_iterator<char*, std::__cxx11::basic_string<char> > >; Attr = std::pair<int, int>]’
/home/pansen/proggs/foo/src/foo/model/routing_parser_test.cpp:23:46:   required from here
/usr/include/boost/spirit/home/qi/nonterminal/rule.hpp:304:17: error: no match for call to ‘(const function_type {aka const boost::function<bool(__gnu_cxx::__normal_iterator<char*, std::__cxx11::basic_string<char> >&, const __gnu_cxx::__normal_iterator<char*, std::__cxx11::basic_string<char> >&, boost::spirit::context<boost::fusion::cons<std::pair<int, int>&, boost::fusion::nil_>, boost::fusion::vector0<> >&, const boost::spirit::qi::char_class<boost::spirit::tag::char_code<boost::spirit::tag::space, boost::spirit::char_encoding::ascii> >&)>}) (__gnu_cxx::__normal_iterator<char*, std::__cxx11::basic_string<char> >&, const __gnu_cxx::__normal_iterator<char*, std::__cxx11::basic_string<char> >&, boost::spirit::qi::rule<__gnu_cxx::__normal_iterator<char*, std::__cxx11::basic_string<char> >, std::pair<int, int>(), boost::proto::exprns_::expr<boost::proto::tagns_::tag::terminal, boost::proto::argsns_::term<boost::spirit::tag::char_code<boost::spirit::tag::space, boost::spirit::char_encoding::ascii> >, 0l>, boost::spirit::unused_type, boost::spirit::unused_type>::context_type&, const boost::spirit::unused_type&)’
                 if (f(first, last, context, skipper))
                 ^
In file included from /usr/include/boost/function/detail/maybe_include.hpp:33:0,
                 from /usr/include/boost/function/detail/function_iterate.hpp:14,
                 from /usr/include/boost/preprocessor/iteration/detail/iter/forward1.hpp:67,
                 from /usr/include/boost/function.hpp:64,
                 from /usr/include/boost/spirit/home/qi/nonterminal/rule.hpp:16,
                 from /usr/include/boost/spirit/home/qi/nonterminal.hpp:14,
                 from /usr/include/boost/spirit/home/qi.hpp:21,
                 from /usr/include/boost/spirit/include/qi.hpp:16,
                 from /home/pansen/proggs/foo/src/foo/model/routing_parser_test.cpp:2:
/usr/include/boost/function/function_template.hpp:767:17: note: candidate: boost::function4<R, T1, T2, T3, T4>::result_type boost::function4<R, T1, T2, T3, T4>::operator()(T0, T1, T2, T3) const [with R = bool; T0 = __gnu_cxx::__normal_iterator<char*, std::__cxx11::basic_string<char> >&; T1 = const __gnu_cxx::__normal_iterator<char*, std::__cxx11::basic_string<char> >&; T2 = boost::spirit::context<boost::fusion::cons<std::pair<int, int>&, boost::fusion::nil_>, boost::fusion::vector0<> >&; T3 = const boost::spirit::qi::char_class<boost::spirit::tag::char_code<boost::spirit::tag::space, boost::spirit::char_encoding::ascii> >&; boost::function4<R, T1, T2, T3, T4>::result_type = bool]
     result_type operator()(BOOST_FUNCTION_PARMS) const
                 ^
/usr/include/boost/function/function_template.hpp:767:17: note:   no known conversion for argument 4 from ‘const boost::spirit::unused_type’ to ‘const boost::spirit::qi::char_class<boost::spirit::tag::char_code<boost::spirit::tag::space, boost::spirit::char_encoding::ascii> >&’

The error points to if (f(first, last, context, skipper)) which looks like the error here (see answer by sehe). But I already correctly specify the attribute (at least I think so).

Answer 1

If you wish to use a skipper, you must pass an instance of it, by calling phrase_parse instead of parse:

bool r = phrase_parse(s.begin(), s.end(), grammar, qi::space, p);

Alternatively, you can hide the details about the skipper by declaring it in a enclosing skipper-less rule with skip(qi::space) [ real_start_rule_with_skipper ]

See also: Boost spirit skipper issues

Notes:

• do not use using namespace - especially not both std and boost::spirit::qi at the same time. You can always use using namespace qi; locally

• no need to wrap every literal in lit(). Here's the rule simplified:

  position_rule = '(' >> qi::int_ >> ',' >> qi::int_ >> ')';
  

DEMO

Live On Coliru

#include <boost/spirit/include/qi.hpp>
#include <boost/fusion/include/std_pair.hpp>

namespace qi = boost::spirit::qi;

using position = std::pair<int, int>;

template <typename Iterator> struct position_grammar : qi::grammar<Iterator, position()> {
    position_grammar() : position_grammar::base_type(start) {

        position_rule = '(' >> qi::int_ >> ',' >> qi::int_ >> ')';
        start         = qi::skip(boost::spirit::ascii::space) [ position_rule ];

    }
    qi::rule<Iterator, position()> start;
    qi::rule<Iterator, position(), boost::spirit::ascii::space_type> position_rule;
};

int main() {
    std::string s = "  ( 1\t,\r\n2 )";
    position_grammar<std::string::iterator> grammar;
    position p;

    bool r = parse(s.begin(), s.end(), grammar, p);

    std::cout << "parsing: " << r << " position: " << p.first << ", " << p.second << "\n";
}

Prints

parsing: 1 position: 1, 2