boost_1_45_0/libs/spirit/example/qi/key_value_sequence_empty_value.cpp

//  Copyright (c) 2001-2010 Hartmut Kaiser
// 
//  Distributed under the Boost Software License, Version 1.0. (See accompanying 
//  file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)

// The purpose of this example is to show how to parse arbitrary key/value 
// pairs delimited by some separator into a std::vector. The difference to 
// the example 'key_value_sequence.cpp' is that we preserve the order of the
// elements in the parsed sequence as well as possibly existing duplicates.
// In addition to the example 'key_value_sequence_ordered.cpp' we allow for 
// empty values, i.e. the grammar allows to distinguish between 'key=;' and
// 'key;", where the first stores an empty string as the value, while the 
// second does not initialize the optional holding the value.
//
// For a more elaborate explanation see here: http://spirit.sourceforge.net/home/?p=371

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

#include <iostream>
#include <map>

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

    typedef std::pair<std::string, boost::optional<std::string> > pair_type;
    typedef std::vector<pair_type> pairs_type;

    template <typename Iterator>
    struct key_value_sequence_empty_value
      : qi::grammar<Iterator, pairs_type()>
    {
        key_value_sequence_empty_value()
          : key_value_sequence_empty_value::base_type(query)
        {
            query =  pair >> *((qi::lit(';') | '&') >> pair);
            pair  =  key >> -('=' >> -value);
            key   =  qi::char_("a-zA-Z_") >> *qi::char_("a-zA-Z_0-9");
            value = +qi::char_("a-zA-Z_0-9");
        }

        qi::rule<Iterator, pairs_type()> query;
        qi::rule<Iterator, pair_type()> pair;
        qi::rule<Iterator, std::string()> key, value;
    };
}

///////////////////////////////////////////////////////////////////////////////
int main()
{
    namespace qi = boost::spirit::qi;

    std::string input("key1=value1;key2;key3=value3;key4=");
    std::string::iterator begin = input.begin();
    std::string::iterator end = input.end();

    client::key_value_sequence_empty_value<std::string::iterator> p;
    client::pairs_type m;

    if (!qi::parse(begin, end, p, m))
    {
        std::cout << "-------------------------------- \n";
        std::cout << "Parsing failed\n";
        std::cout << "-------------------------------- \n";
    }
    else
    {
        std::cout << "-------------------------------- \n";
        std::cout << "Parsing succeeded, found entries:\n";
        client::pairs_type::iterator end = m.end();
        for (client::pairs_type::iterator it = m.begin(); it != end; ++it)
        {
            std::cout << (*it).first;
            if ((*it).second)
                std::cout << "=" << boost::get<std::string>((*it).second);
            std::cout << std::endl;
        }
        std::cout << "---------------------------------\n";
    }
    return 0;
}