Compiling simple boost spirit grammar

Question

I'm having trouble getting a small boost::spirit grammar to compile. It's a small part of a larger grammar that I'm having trouble with and I'm trying to test smaller parts to find my problem. Basicly what this grammar should do is parse a double value which has any number of leading/trailing spaces. However when I try to compile I get a whole list of problems which I don't understand. Any help would be welcome! The code: grammar.h

#ifndef GRAMMAR_H
#define GRAMMAR_H

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

template <typename Iterator>
struct point_double_grammar : boost::spirit::qi::grammar<Iterator, double()>
{
    /**
     * Constructor used to create the grammar.
     * @param   is_point            boolean indicating if the point is used as decimal.
     * @author  Luc Kleeven
     **/
    point_double_grammar() : point_double_grammar::base_type(d)
    {
        d = *boost::spirit::qi::lit(' ') >> boost::spirit::qi::double_ >> *boost::spirit::qi::lit(' ');
    }
    boost::spirit::qi::rule<Iterator, double()> d;
};

#endif // GRAMMAR_H

main.cpp

#include "grammar.h"

int main(int argc, char *argv[])
{
    point_double_grammar<std::string::iterator> point_grammar();

    bool result = false;
    double d = 0.0;
    std::string p1 = "575040.3400";
    std::string p2 = "117380.1200";
    std::string p3 = "-001.22916765";
    std::string p4 = "063.39171738";
    std::string p5 = "2.5";

    std::string::iterator it;
    std::string::iterator last;

    it = p1.begin();
    last = p1.end();
    result = (boost::spirit::qi::parse(it, last, point_grammar, d) && it ==
            last);
    if(result)
    {
        std::cout << p1 << " == " << d << std::endl;
    }
    else
    {
        std::cout << "Parsing failed!" << std::endl;
    }

    it = p2.begin();
    last = p2.end();
    result = (boost::spirit::qi::parse(it, last, point_grammar, d) && it ==
            last);
    if(result)
    {
        std::cout << p2 << " == " << d << std::endl;
    }
    else
    {
        std::cout << "Parsing failed!" << std::endl;
    }

    it = p3.begin();
    last = p3.end();
    result = (boost::spirit::qi::parse(it, last, point_grammar, d) && it == last);
    if(result)
    {
        std::cout << p3 << " == " << d << std::endl;
    }
    else
    {
        std::cout << "Parsing failed!" << std::endl;
    }

    it = p4.begin();
    last = p4.end();
    result = (boost::spirit::qi::parse(it, last, point_grammar, d) && it == last);
    if(result)
    {
        std::cout << p4 << " == " << d << std::endl;
    }
    else
    {
        std::cout << "Parsing failed!" << std::endl;
    }

    it = p5.begin();
    last = p5.end();
    result = (boost::spirit::qi::parse(it, last, point_grammar, d) && it == last);
    if(result)
    {
        std::cout << p5 << " == " << d << std::endl;
    }
    else
    {
        std::cout << "Parsing failed!" << std::endl;
    }

    return EXIT_SUCCESS;
}

When I try to compile I get the following errors:

In file included from c:\mingw\bin\../lib/gcc/mingw32/4.6.1/../../../../include/boost/spirit/home/qi/detail/parse_auto.hpp:14:0,
                 from c:\mingw\bin\../lib/gcc/mingw32/4.6.1/../../../../include/boost/spirit/home/qi/auto.hpp:16,
                 from c:\mingw\bin\../lib/gcc/mingw32/4.6.1/../../../../include/boost/spirit/home/qi.hpp:15,
                 from c:\mingw\bin\../lib/gcc/mingw32/4.6.1/../../../../include/boost/spirit/include/qi.hpp:16,
                 from ../test/grammar.h:4,
                 from ../test/main.cpp:1:
c:\mingw\bin\../lib/gcc/mingw32/4.6.1/../../../../include/boost/spirit/home/qi/parse.hpp: In function 'bool boost::spirit::qi::parse(Iterator&, Iterator, const Expr&, Attr&) [with Iterator = __gnu_cxx::__normal_iterator<char*, std::basic_string<char> >, Expr = point_double_grammar<__gnu_cxx::__normal_iterator<char*, std::basic_string<char> > >(), Attr = double]':
../test/main.cpp:20:63:   instantiated from here
c:\mingw\bin\../lib/gcc/mingw32/4.6.1/../../../../include/boost/spirit/home/qi/parse.hpp:83:9: error: no matching function for call to 'assertion_failed(mpl_::failed************ (boost::spirit::qi::parse(Iterator&, Iterator, const Expr&, Attr&) [with Iterator = __gnu_cxx::__normal_iterator<char*, std::basic_string<char> >, Expr = point_double_grammar<__gnu_cxx::__normal_iterator<char*, std::basic_string<char> > >(), Attr = double]::error_invalid_expression::************)(point_double_grammar<__gnu_cxx::__normal_iterator<char*, std::basic_string<char> > > (*)()))'
c:\mingw\bin\../lib/gcc/mingw32/4.6.1/../../../../include/boost/spirit/home/qi/parse.hpp:83:9: note: candidate is:
c:\mingw\bin\../lib/gcc/mingw32/4.6.1/../../../../include/boost/mpl/assert.hpp:79:48: note: template<bool C> int mpl_::assertion_failed(typename mpl_::assert<C>::type)
In file included from c:\mingw\bin\../lib/gcc/mingw32/4.6.1/../../../../include/boost/proto/detail/expr.hpp:6:0,
                 from c:\mingw\bin\../lib/gcc/mingw32/4.6.1/../../../../include/boost/proto/expr.hpp:120,
                 from c:\mingw\bin\../lib/gcc/mingw32/4.6.1/../../../../include/boost/proto/core.hpp:17,
                 from c:\mingw\bin\../lib/gcc/mingw32/4.6.1/../../../../include/boost/proto/proto.hpp:12,
                 from c:\mingw\bin\../lib/gcc/mingw32/4.6.1/../../../../include/boost/spirit/home/support/meta_compiler.hpp:19,
                 from c:\mingw\bin\../lib/gcc/mingw32/4.6.1/../../../../include/boost/spirit/home/qi/meta_compiler.hpp:14,
                 from c:\mingw\bin\../lib/gcc/mingw32/4.6.1/../../../../include/boost/spirit/home/qi/action/action.hpp:14,
                 from c:\mingw\bin\../lib/gcc/mingw32/4.6.1/../../../../include/boost/spirit/home/qi/action.hpp:14,
                 from c:\mingw\bin\../lib/gcc/mingw32/4.6.1/../../../../include/boost/spirit/home/qi.hpp:14,
                 from c:\mingw\bin\../lib/gcc/mingw32/4.6.1/../../../../include/boost/spirit/include/qi.hpp:16,
                 from ../test/grammar.h:4,
                 from ../test/main.cpp:1:
c:\mingw\bin\../lib/gcc/mingw32/4.6.1/../../../../include/boost/proto/detail/preprocessed/expr.hpp: At global scope:
c:\mingw\bin\../lib/gcc/mingw32/4.6.1/../../../../include/boost/proto/detail/preprocessed/expr.hpp: In instantiation of 'boost::proto::exprns_::expr<boost::proto::tagns_::tag::terminal, boost::proto::argsns_::term<point_double_grammar<__gnu_cxx::__normal_iterator<char*, std::basic_string<char> > >()>, 0l>':
c:\mingw\bin\../lib/gcc/mingw32/4.6.1/../../../../include/boost/utility/enable_if.hpp:59:10:   instantiated from 'boost::disable_if<boost::proto::is_expr<boost::proto::exprns_::expr<boost::proto::tagns_::tag::terminal, boost::proto::argsns_::term<point_double_grammar<__gnu_cxx::__normal_iterator<char*, std::basic_string<char> > >()>, 0l>, void>, void>'
c:\mingw\bin\../lib/gcc/mingw32/4.6.1/../../../../include/boost/spirit/home/support/meta_compiler.hpp:212:16:   instantiated from 'boost::spirit::result_of::compile<boost::spirit::qi::domain, point_double_grammar<__gnu_cxx::__normal_iterator<char*, std::basic_string<char> > >(), boost::spirit::unused_type, void>'
c:\mingw\bin\../lib/gcc/mingw32/4.6.1/../../../../include/boost/spirit/home/qi/parse.hpp:86:82:   instantiated from 'bool boost::spirit::qi::parse(Iterator&, Iterator, const Expr&, Attr&) [with Iterator = __gnu_cxx::__normal_iterator<char*, std::basic_string<char> >, Expr = point_double_grammar<__gnu_cxx::__normal_iterator<char*, std::basic_string<char> > >(), Attr = double]'
../test/main.cpp:20:63:   instantiated from here
c:\mingw\bin\../lib/gcc/mingw32/4.6.1/../../../../include/boost/proto/detail/preprocessed/expr.hpp:50:49: error: field 'boost::proto::exprns_::expr<boost::proto::tagns_::tag::terminal, boost::proto::argsns_::term<point_double_grammar<__gnu_cxx::__normal_iterator<char*, std::basic_string<char> > >()>, 0l>::child0' invalidly declared function type
In file included from c:\mingw\bin\../lib/gcc/mingw32/4.6.1/../../../../include/boost/spirit/home/qi/detail/parse_auto.hpp:14:0,
                 from c:\mingw\bin\../lib/gcc/mingw32/4.6.1/../../../../include/boost/spirit/home/qi/auto.hpp:16,
                 from c:\mingw\bin\../lib/gcc/mingw32/4.6.1/../../../../include/boost/spirit/home/qi.hpp:15,
                 from c:\mingw\bin\../lib/gcc/mingw32/4.6.1/../../../../include/boost/spirit/include/qi.hpp:16,
                 from ../test/grammar.h:4,
                 from ../test/main.cpp:1:
c:\mingw\bin\../lib/gcc/mingw32/4.6.1/../../../../include/boost/spirit/home/qi/parse.hpp: In function 'bool boost::spirit::qi::parse(Iterator&, Iterator, const Expr&, Attr&) [with Iterator = __gnu_cxx::__normal_iterator<char*, std::basic_string<char> >, Expr = point_double_grammar<__gnu_cxx::__normal_iterator<char*, std::basic_string<char> > >(), Attr = double]':
../test/main.cpp:20:63:   instantiated from here
c:\mingw\bin\../lib/gcc/mingw32/4.6.1/../../../../include/boost/spirit/home/qi/parse.hpp:86:82: error: request for member 'parse' in 'boost::spirit::compile [with Domain = boost::spirit::qi::domain, Expr = point_double_grammar<__gnu_cxx::__normal_iterator<char*, std::basic_string<char> > >(), typename boost::spirit::result_of::compile<Domain, Expr, boost::spirit::unused_type>::type = point_double_grammar<__gnu_cxx::__normal_iterator<char*, std::basic_string<char> > > (&)()]((* & expr))', which is of non-class type 'point_double_grammar<__gnu_cxx::__normal_iterator<char*, std::basic_string<char> > >()'

Note that I'm compiling using boost 1.48.0 and mingw 4.6.1 on a windows 7 machine.

Answer 1

Change this line:

point_double_grammar<std::string::iterator> point_grammar();

To:

point_double_grammar<std::string::iterator> point_grammar;

You've declared a function taking no arguments that returns a grammar. Instead, you want to instantiate the grammar.

Answer 2

Sharth has already answered your question, you should accept that answer of course.

I wanted to share a few other things, you might find helpful.

• as I mentioned: format your code (code is for humans)
• Try using a loop instead of duplicating your code. You weren't parsing a list of doubles. You were parsing a single double, 5 times
• Avoid C-isms (declare and initialize at the top?)
• Look at Qi Skippers: you were manually 'ignoring' whitespace. Qi has Skippers for that purpose (see qi::phrase_parse in below sample)
• Consider using Boost Karma for output generation. At least use <iomanip> to control the output format (see std::setprecision below)

Here is the full example

#include <boost/spirit/include/qi.hpp>
#include <iomanip>
namespace qi = boost::spirit::qi;

template <typename Iterator, typename Skipper>
struct point_double_grammar : qi::grammar<Iterator, double(), Skipper>
{
    point_double_grammar() : point_double_grammar::base_type(d)
    {
        d = qi::double_;
    }

    qi::rule<Iterator, double(), Skipper> d;
};

static const char *const testcases[] = {
    "575040.3400",
    "117380.1200",
    "-001.22916765",
    "063.39171738",
    "2.5", 
    NULL
};

int main()
{
    typedef std::string::const_iterator It;
    point_double_grammar<It, qi::space_type> point_grammar;

    for(const char* const* it=testcases; *it; ++it)
    {
        const std::string input(*it);
        It it = input.begin(), last = input.end();

        double d = 0.0;
        bool result = (qi::phrase_parse(it, last, point_grammar, qi::space, d) && it ==
                last);

        if(result)
            std::cout << input << " == "
                     << std::setprecision(10) << d << std::endl;
        else
            std::cerr << "Parsing failed!" << std::endl;
    }
}

With C++11 you'd even write:

for (const std::string input : { 
        "575040.3400", "117380.1200", "-001.22916765", "063.39171738", "2.5" })
{
    auto it = input.begin(), last = input.end();

etc. For the record, the output is:

575040.3400 == 575040.34
117380.1200 == 117380.12
-001.22916765 == -1.22916765
063.39171738 == 63.39171738
2.5 == 2.5

Without std::setprecision(10) the output would be, e.g. 575040.3400 == 575040 for the first line. Consider using Boost Karma for output generation.