#include <fstream>
#include <iostream>
#include <iterator>
#include <algorithm>
#include <locale>

struct codecvt_test : std::codecvt<wchar_t, char, std::mbstate_t> 
{
    codecvt_test(std::size_t refs = 0) : std::codecvt<wchar_t, char, std::mbstate_t>(refs)
    {
    }
    
protected:
    virtual std::codecvt_base::result do_unshift(std::mbstate_t &s,char *from,char *to,char *&next) const
    {
        return std::codecvt_base::ok;
    }
    virtual int do_encoding() const throw()
    {
        return 0;
    }
    virtual int do_max_length() const throw()
    {
        return 42;
    }
    virtual bool do_always_noconv() const throw()
    {
        return false;
    }
        
    virtual std::codecvt_base::result 
    do_in(  std::mbstate_t &state,
            char const *from,
            char const *from_end,
            char const *&from_next,
            wchar_t *uto,
            wchar_t *uto_end,
            wchar_t *&uto_next) const
    {
        *uto++ = L'A';
        *uto++ = L'B';
        uto_next = uto;
        from_next = from_end;
        return std::codecvt_base::ok;
    }
        
    virtual int
    do_length(  std::mbstate_t &state,
                char const *from,
                char const *from_end,
                size_t max) const
    {
        return 42;
    }

    virtual std::codecvt_base::result 
    do_out( std::mbstate_t &state,
            wchar_t const *ufrom,
            wchar_t const *ufrom_end,
            wchar_t const *&ufrom_next,
            char *to,
            char *to_end,
            char *&to_next) const
    {
        return std::codecvt_base::ok;
    }
};

int main()
{
    std::locale old_loc;
    std::locale loc(old_loc, new codecvt_test);
    
    {
        std::fstream f("test.tmp", std::ios_base::out | std::ios_base::trunc);
        f << "foobar" << std::endl;
    }
    
    {
        std::wfstream f("test.tmp");
        f.imbue(loc);
        std::copy(std::istream_iterator<wchar_t, wchar_t>(f), std::istream_iterator<wchar_t, wchar_t>(), std::ostream_iterator<wchar_t, char>(std::cout, " "));
        std::cout << std::endl;
    }
}