CODEWITHSUNDEEP
c++parsingboostc++14boost-spirit
Quentin
Quentin

Reputation: 63154

Boost.Spirit.Qi alternative ( | ) parser issue

I'm writing a Qi parser to parse IRC messages, transcribing RFC 2812. Among the grammar is a completely mundate alternative :

auto const hostname = shortname >> *('.' >> shortname);
auto const nickUserHost = nickname >> -(-('!' >> user) >> '@' >> host);

auto const prefix = hostname | nickUserHost;

(Full code on Coliru here)

I'm baffled to see that my test string ("[email protected]") matches nickUserHost, but not prefix.

The only remarkable thing that I see is that nickUserHost's host is itself defined in terms of hostname, but I'm not sure how it would affect the parsing in any way.

Upvotes: 2

Views: 188

Answers (1)

sehe
sehe

Reputation: 393789

By appending >> eoi you explicitly make the parse failed if it didn't reach the end of the input.

Live On Coliru

#include <string>
#include <iostream>
#include <iomanip>

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

namespace qi = boost::spirit::qi;

template <typename Expr>
void test(std::string name, Expr const& expr) {
    std::string const test = "[email protected]";

    auto f = begin(test);
    bool ok = qi::parse(f, end(test), expr);
    std::cout << name << ": " << ok << "\n";
    if (f != end(test))
        std::cout << " -- remaining input: '" << std::string(f, end(test)) << "'\n";
}

int main() {
    auto const hexdigit = qi::char_("0123456789ABCDEF");
    auto const special = qi::char_("\x5b-\x60\x7b-\x7d");

    auto const oneToThreeDigits = qi::repeat(1, 3)[qi::digit];
    auto const ip4addr = oneToThreeDigits >> '.' >> oneToThreeDigits >> '.' >> oneToThreeDigits >> '.' >> oneToThreeDigits;
    auto const ip6addr = +(hexdigit >> qi::repeat(7)[':' >> +hexdigit]) | ("0:0:0:0:0:" >> (qi::lit('0') | "FFFF") >> ':' >> ip4addr);
    auto const hostaddr = ip4addr | ip6addr;

    auto const nickname = (qi::alpha | special) >> qi::repeat(0, 8)[qi::alnum | special | '-'];
    auto const user = +(~qi::char_("\x0d\x0a\x20\x40"));

    auto const shortname = qi::alnum >> *(qi::alnum | '-');
    auto const hostname = shortname >> *('.' >> shortname);
    auto const host = hostname | hostaddr;

    auto const nickUserHost = nickname >> -(-('!' >> user) >> '@' >> host);

    auto const prefix = hostname | nickUserHost; // The problematic alternative

    std::cout << std::boolalpha;
    test("hostname",     hostname);
    test("nickUserHost", nickUserHost);
    test("prefix",       prefix);
}

Prints

hostname: true
-- remaining input: '[email protected]'
nickUserHost: true
prefix: true
-- remaining input: '[email protected]'

Upvotes: 2

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