Parsing hex values with Boost Spirit

I have been playing around with parsing with Boost Spirit and was wondering if anyone could help me get this to work. I have a simple parser that takes a file containing a pair of entries on each line. Something similar to the following:

Foo 04B
Bar 1CE
Bam 456

My code below currently parses this out and places each pair into a std::map and it seems to work correctly. What I really want to do is parse out the second string on each line and convert it to an integer. I have looked at int_parser and how you can specify the base but have been unable to get a similar setup to compile.

namespace qi = boost::spirit::qi;
std::map results;




void insert(std::pair p) {
    results[p.first] = p.second;
}




template 
bool parse_numbers(Iterator first, Iterator last) {
    using qi::char_;
    using qi::parse;

    qi::rule<Iterator, std::pair<std::string, std::string>()> assignment;
    assignment = +(~char_(' '))  >> +(char_);

    bool r = parse(
    first,
    last,
    assignment[&insert]);

    if (first != last)
        return false;

    return r;
}

int main(int argc, char* argv[]) {
    std::ifstream ifs;
    std::string str;
    ifs.open (argv[1], std::ifstream::in);

    while (getline(ifs, str)) {
        if (!parse_numbers(str.begin(), str.end())) {
            std::cout << "Parsing failed\n";
        }
    }

    return 0;
}

What I would really like if to parse it out directly as a std::pair<std::string, int>. Any help is appreciated.