Boost.Spirit parse string to number with radix

Question

I have a template function which casts string to number as following:

template <typename RetType,
    typename Parser =
    typename boost::spirit::traits::create_parser<RetType>::type>
    inline std::enable_if_t<std::is_arithmetic<RetType>::value, RetType>
    cast(const std::string &input)
{
    RetType result;

    if(input.empty())
    {
        // handle this
    }
    auto itBeg = input.cbegin();
    auto itEnd = input.cend();
    if(!bsq::parse(itBeg, itEnd, Parser(), result) || itBeg != itEnd)
    {
        // handle that
    }
    return result;
}

now I would like to create a function similar to above which will parse string that represents a number in some radix

template <typename RetType, unsigned Radix,
    typename Parser =
    typename boost::spirit::traits::create_parser<RetType>::type>
    inline std::enable_if_t<std::is_arithmetic<RetType>::value, RetType>
    cast(const std::string &input)
{
    RetType result;

    if(input.empty())
    {
        // handle this
    }
    auto itBeg = input.cbegin();
    auto itEnd = input.cend();
    if(!bsq::parse(itBeg, itEnd, Parser<RetType, Radix, 1 - 1>() /*something like this*/, result) || itBeg != itEnd)
    {
        // handle that
    }

    return result;
}

the Parser is invalid, of course, but what is the right way to define "automatic" arithmetic parser with radix?

Answer 1

I'd use qi::int_parser<> directly:

Live On Coliru

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

template <typename RetType, unsigned Radix = 10, typename Parser = typename boost::spirit::qi::int_parser<RetType, Radix> >
inline typename std::enable_if<std::is_arithmetic<RetType>::value, RetType>::type
    cast(const std::string &input)
{
    RetType result;

    if(input.empty())
    {
        // handle this
    }
    auto itBeg = input.cbegin();
    auto itEnd = input.cend();
    if(!boost::spirit::qi::parse(itBeg, itEnd, Parser(), result) || itBeg != itEnd)
    {
        // handle that
        throw "oops";
    }

    return result;
}

int main() {
    std::cout << cast<int>    ("10") << "\n";
    std::cout << cast<int,  2>("10") << "\n";
    std::cout << cast<int,  8>("10") << "\n";
    std::cout << cast<int, 16>("10") << "\n";
    std::cout << cast<int, 16>("ee") << "\n";
}

Prints

10
2
8
16
238

Hint: to be very accurate you might want to detect signed/unsigned types and use uint_parser<> accordingly