Question

I am learning Boost Spirit and simply modified an example given in the documentation to match strings instead of doubles. But the code doesn’t compile and I get errors which I am unable to debug. Below is the code and the printed errors. Can you please help me debug this problem ?

PS: I am guessing the problem lies in using phoenix::ref for vector string, but not exactly sure how and why.

#include <boost/spirit/include/qi.hpp>
#include <boost/spirit/include/phoenix_core.hpp>
#include <boost/spirit/include/phoenix_operator.hpp>
#include <boost/spirit/include/phoenix_stl.hpp>
#include <boost/config/warning_disable.hpp>

#include <iostream>
#include <string>
#include <vector>

namespace client
{
    namespace qi = boost::spirit::qi;
    namespace ascii = boost::spirit::ascii;
    namespace phoenix = boost::phoenix;

    template <typename Iterator>

    bool parse_data(Iterator first, Iterator last, std::vector<std::string>& v)
    {
        using qi::double_;
        using qi::char_;
        using qi::phrase_parse;
        using qi::_1;
        using ascii::space;
        using phoenix::ref;
        using phoenix::push_back;

        bool r = phrase_parse(
            first,
            last,
            +(char_)[push_back(ref(v), _1)],        
            char_('/')  
        );
        if (first != last)
            return false;
        return r;
    }
}

int 
main()
{
    std::string str;

    while (getline(std::cin, str))
    {
        if (str.empty())
            break;

        std::vector<std::string> v;
        if(client::parse_data(str.begin(), str.end(), v))
        {
            std::cout << std::endl << "Parsing done" << std::endl;
            std::cout << "Numbers are " ;
            for(std::vector<std::string>::iterator i = v.begin(); i < v.end(); i++)
            {
                std::cout << *i <<" ";
            }
            std::cout << std::endl;
        }
        else
        {
            std::cout << "Parsing Failed" << std::endl;
        }
    }

    return 0;
}

This is the error I get:

/usr/local/include/boost_1_46_1/boost/spirit/home/phoenix/stl/container/container.hpp:492:
error: invalid conversion from ‘const char’ to ‘const char*’

/usr/local/include/boost_1_46_1/boost/spirit/home/phoenix/stl/container/container.hpp:492: 
error:   initializing argument 1 of ‘std::basic_string<_CharT, _Traits, _Alloc>::basic_string(const _CharT*, const _Alloc&) [with _CharT = char, _Traits = std::char_traits<char>, _Alloc = std::allocator<char>]’

Answer 1

If you write it as

bool r = phrase_parse(
    first, last, +(char_[push_back(ref(v), _1)]), char_('/')  
);

it will work. But writing

bool r = phrase_parse(
    first, last, +char_, '/', v
);

is even simpler (and runs faster).