Question

This is my custom string class (xstring.hpp):

#include <vector>
#include <sstream>

namespace
{
    using std::vector;
    using std::istringstream;

    template <class strT>
    class xstring_base
    {
        private:
            strT str;

        public:
            operator strT&() {return str;}
            vector<strT>* tokenize();

            // constructors
            xstring_base<strT>(strT);
    };
}
#include "xstring.cpp"

#include <string>
typedef xstring_base<std::string> xstring;

I’ve put the operator strT&() to mimic the Standard Library’s string behavior wherever needed, and this class works absolutely fine when I initialize it with a C-style string, even containing non-ASCII code, for example arabic, but std::getline complains that xstring is not supported.

How can I use getline to input from cin to this custom string class of mine?

(I use g++ on Kubuntu 11.10. Gives tens of lines of complain about template mixture mismatches…)

Thanks so much!

Answer 1

std::getline is a function template that looks like this:

template< class CharT, class Traits, class Allocator >
std::basic_istream<CharT,Traits>& getline( std::basic_istream<CharT,Traits>& input,
                                           std::basic_string<CharT,Traits,Allocator>& str );

When you call std::getline(std::cin, x), you don’t provide template arguments. This means that the types will have to be deduced from the arguments.

However, the type deduction algorithm does not take user-defined conversions into account. So your conversion operator is not used. If you wrote std::getline<char, std::char_traits<char>, std::allocator<char>>(std::cin, x), no type deduction is needed, so the conversion operator would be considered.