boost::spirit::qi - whats wrong with this hex parse?

Question

Consider following code:

{
        std::string input = "FFFFFFF";
        int result = 0;
        auto itBeg = input.cbegin();
        auto itEnd = input.cend();
        if(!bsq::parse(itBeg, itEnd, bsq::int_parser<int, 16>(), result) || itBeg != itEnd)
        {
            throw std::exception();
        }
        std::cout << input << " means " << result << std::endl;
    }
    {
        std::string input = "FFFFFFFF";
        int result = 0;
        auto itBeg = input.cbegin();
        auto itEnd = input.cend();
        if(!bsq::parse(itBeg, itEnd, bsq::hex, result) || itBeg != itEnd)
        {
            throw std::exception();
        }
        std::cout << input << " means " << result << std::endl;
    }
    {
        std::string input = "FFFFFFFF";
        int result = 0;
        auto itBeg = input.cbegin();
        auto itEnd = input.cend();
        if(!bsq::parse(itBeg, itEnd, bsq::int_parser<int, 16>(), result) || itBeg != itEnd)
        {
            throw std::exception();
        }
        std::cout << input << " means " << result << std::endl;
    }

the first parse works fine on 0xFFFFFFF (note, 7 hex digits) second one works ok on 0xFFFFFFFF (8 hex digits) the third one fails and I cant understand why. isnt int_parser<T, 16> is essentially the same as bsq::hex?
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Answer 1

the third one fails and I cant understand why

You're using a signed parser, and hitting a type width boundary. Change it to:

bsq::uint_parser<unsigned int, 16>(), result)

(live demo)

---

isnt int_parser<T, 16> is essentially the same as bsq::hex?

No.

The documentation says that boost::spirit::qi::hex will

Parse an unsigned integer using [..] radix 16