Question

I have a strange problem with a calculator made using boost::spirit. This calculator is supposed to take a string as argument representing a series of arithmetical expression separated by commas, like “a+4*5,77,(b-c)*4”. It also allows the string “?” and returns the array containing a -1 in this case. The calculator is initialized with a SymTable, which is a template class argument to describe any class offering the [string] -> int operator (example: a map), to resolve the value of variables.

The following code works on my Ubuntu 10.4 with both gcc 4.6.2 and gcc 4.4, and both boost 1.47 and 1.48. It also worked in the past on a Cray Linux machine with gcc 4.5.3 and boost 1.47.

#include <boost/bind.hpp>
#include <boost/spirit/include/qi.hpp>
#include <boost/spirit/include/phoenix_core.hpp>
#include <boost/spirit/include/phoenix_operator.hpp>

namespace sp = boost::spirit;
namespace qi = boost::spirit::qi;
namespace ascii = boost::spirit::ascii;

namespace Damaris {

template <typename Iterator, typename SymTable>
struct Calc : qi::grammar<Iterator, std::vector<int>(), ascii::space_type>
{
        qi::rule<Iterator, std::vector<int>(), ascii::space_type> start;
        qi::rule<Iterator, int(), ascii::space_type> expr;
        qi::rule<Iterator, int(), ascii::space_type> qmark;
        qi::rule<Iterator, int(), ascii::space_type> factor;
        qi::rule<Iterator, int(), ascii::space_type> simple;
        qi::rule<Iterator, std::string(), ascii::space_type> identifier;
        qi::rule<Iterator, int(SymTable), ascii::space_type> value;

        /**
         * \brief Constructor.
         * \param[in] sym : table of symboles.
         */
        Calc(SymTable &sym) : Calc::base_type(start)
        {
                identifier = qi::lexeme[( qi::alpha | '_') >> *( qi::alnum | '_')];

                value   = identifier[qi::_val = qi::labels::_r1[qi::_1]];

                simple  = ('(' >> expr >> ')')
                        | qi::int_
                        | value(boost::phoenix::ref(sym));

                factor  %= (simple >> '*' >> factor)[qi::_val = qi::_1 * qi::_2]
                        |  (simple >> '/' >> factor)[qi::_val = qi::_1 / qi::_2]
                        |  (simple >> '%' >> factor)[qi::_val = qi::_1 % qi::_2]
                        |   simple;

                expr    %= (factor >> '+' >> expr)[qi::_val = qi::_1 + qi::_2]
                        |  (factor >> '-' >> expr)[qi::_val = qi::_1 - qi::_2]
                        |   factor;

                qmark   = qi::char_('?')[qi::_val = -1];

                start   = qmark
                        | (expr % ',');
        }
};

}

Today I tried again compiling the same code on the Cray machine (which has been upgraded since then, I think), I tried with gcc 4.6.2 and gcc 4.5.2, and both with boost 1.48 and 1.49, and I always get the same compilation error that I don’t understand :

/nics/b/home/mdorier/damaris-0.4/common/Calc.hpp:74:3:   instantiated from 'Damaris::Calc<Iterator, SymTable>::Calc(SymTable&) [with Iterator = __gnu_cxx::__normal_iterator<const char*, std::basic_string<char> >, SymTable = Damaris::ParameterSet]'
/nics/b/home/mdorier/damaris-0.4/common/MetadataManager.cpp:45:79:   instantiated from here
/nics/b/home/mdorier/deploy/include/boost/spirit/home/qi/detail/assign_to.hpp:123:13: error: invalid static_cast from type 'const boost::fusion::vector2<int, int>' to type 'int'

The line 74 in Calc.hpp corresponds to the line “factor = …”.
The instantiation line indicated (MetadataManager.cpp:45) is the following:

layoutInterp = new Calc<std::string::const_iterator,ParameterSet>(*parameters);

with layoutInterp being of type Calc* and parameters being of type ParameterSet*.

Any idea where this error comes from? Thanks

Answer 1

I’m pretty sure you might have been rearranging stuff in your rules. In fact, the %= auto-rule expression assignments won’t work because the synthesized type of the parser expression doesn’t resemble an int.

Basically, you’d change

factor %= (simple >> '*' >> factor)[ _val = _1 * _2 ]
    |  (simple >> '/' >> factor)[ _val = _1 / _2 ]
    |  (simple >> '%' >> factor)[ _val = _1 % _2 ]
    |   simple;

expr   %= (factor >> '+' >> expr)[ _val = _1 + _2 ]
    |  (factor >> '-' >> expr)[ _val = _1 - _2 ]
    |   factor;

into

factor  = (simple >> '*' >> factor)[ _val = _1 * _2 ]
        | (simple >> '/' >> factor)[ _val = _1 / _2 ]
        | (simple >> '%' >> factor)[ _val = _1 % _2 ]
        | (simple) [_val = _1 ];

expr    = (factor >> '+' >> expr)[ _val = _1 + _2 ]
        | (factor >> '-' >> expr)[ _val = _1 - _2 ]
        | (factor) [_val = _1 ];

I have fixed up some small issues and created a SSCCE of your post that works, as far as I can tell ¹:

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

namespace sp = boost::spirit;
namespace qi    = boost::spirit::qi;
namespace ascii = boost::spirit::ascii;
namespace karma = boost::spirit::karma;
namespace phx   = boost::phoenix;

namespace Damaris {

    template <typename Iterator, typename SymTable>
    struct Calc : qi::grammar<Iterator, std::vector<int>(), ascii::space_type>
    {
        qi::rule<Iterator, std::vector<int>(), ascii::space_type> start;
        qi::rule<Iterator, int(), ascii::space_type> expr;
        qi::rule<Iterator, int(), ascii::space_type> qmark;
        qi::rule<Iterator, int(), ascii::space_type> factor;
        qi::rule<Iterator, int(), ascii::space_type> simple;
        qi::rule<Iterator, std::string(), ascii::space_type> identifier;
        qi::rule<Iterator, int(SymTable), ascii::space_type> value;

        Calc(SymTable &sym) : Calc::base_type(start)
        {
            using namespace qi;

            identifier = lexeme[( alpha | '_') >> *( alnum | '_')];

            value   = identifier[ _val = _r1[_1] ];

            simple  = ('(' >> expr >> ')')
                    | int_
                    | value(boost::phoenix::ref(sym));

            factor  = (simple >> '*' >> factor)[ _val = _1 * _2 ]
                    | (simple >> '/' >> factor)[ _val = _1 / _2 ]
                    | (simple >> '%' >> factor)[ _val = _1 % _2 ]
                    | (simple) [_val = _1 ];

            expr    = (factor >> '+' >> expr)[ _val = _1 + _2 ]
                    | (factor >> '-' >> expr)[ _val = _1 - _2 ]
                    | (factor) [_val = _1 ];

            qmark   = char_('?')[ _val = -1 ];

            start   = qmark 
                | (expr % ',');

            BOOST_SPIRIT_DEBUG_NODE(start);
            BOOST_SPIRIT_DEBUG_NODE(qmark);
            BOOST_SPIRIT_DEBUG_NODE(expr);
            BOOST_SPIRIT_DEBUG_NODE(factor);
            BOOST_SPIRIT_DEBUG_NODE(simple);
            BOOST_SPIRIT_DEBUG_NODE(value);
            BOOST_SPIRIT_DEBUG_NODE(identifier);
        }
    };

}

int main(int argc, const char *argv[])
{
    typedef std::map<std::string, int> SymTable;
    SymTable symbols;
    Damaris::Calc<std::string::const_iterator, SymTable> calc(symbols);

    symbols["TheAnswerToLifeUniverse"] = 100;
    symbols["Everything"] = -58;

    std::string input = "3*4+5/4, TheAnswerToLifeUniverse + Everything";
    std::string::const_iterator f(input.begin()), l(input.end());
    std::vector<int> data;

    if (qi::phrase_parse(f,l,calc,ascii::space,data))
        std::cout << "output: " << karma::format(karma::int_ % ", " << karma::eol, data);
    else
        std::cout << "problem: '" << std::string(f,l) << "'\n";

    return 0;
}

Output:

output: 13, 42

---

¹ gcc 4.6.1, boost 1_48