使用Boost Spirit解析十六进制值

Question

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<std::string, std::string> results;

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

template <typename Iterator>
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.

More information:

I was trying to declare a parser similar to this one: uint_parser<unsigned, 16> hex_value; and then I was trying to replace the +(char_) in my rule to +(hex_value).

Answer 1

I'm a little confused with everything complicated going on there (especially the semantic action [&insert] which seems to gratuitously use a global variable).

See Boost Spirit: "Semantic actions are evil"? if you're interested in my stance on premature use of semantic actions.

In this case you could just use Boost Fusion adaptation of std::pair<>

#include <boost/fusion/adapted/std_pair.hpp>

and now you can simply assign directly into a map:

    std::map<std::string, int> results;

    if (ifs >> qi::phrase_match(
                (qi::lexeme[+qi::graph] >> qi::int_parser<int, 16>{}) % qi::eol,
                qi::blank, results)
            )

Demo

As you surmised I

• used int_parser<int,16>
• replaced the input file with std::cin for simplicity ( NOTE you didn't check argc ...)
• uses phrase_match as a nice way to parse from input stream iterators implicitly
• parsers multiple lines in one swoop

Live On Coliru

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

namespace qi = boost::spirit::qi;

int main() {
    std::cin.unsetf(std::ios::skipws);

    std::map<std::string, int> results;

    if (std::cin >> qi::phrase_match(
                (qi::lexeme[+qi::graph] >> qi::int_parser<int, 16>{}) % qi::eol,
                qi::blank, results)
       )
    {
        std::cout << "Parse success:\n";
        for(auto& entry : results)
            std::cout << "'" << entry.first << "' -> " << entry.second << "\n";
    } else {
        std::cout << "Parse failed\n";
    }
}

Output:

Parse success:
'Bam' -> 1110
'Bar' -> 462
'Foo' -> 75