conversion of a single wchar_t with toupper

[denkfix]

Hi,

I am trying to convert a single wchar_t to uppercase. In theory it should work as shown below, in practice it does not. I have no idea what I am doing wrong. Any ideas?

Output is:
T
T
?
?

#include <locale>
#include <string>

int main (  )
{
        std::locale loc ( "en_US.UTF-8" );
        //std::locale loc ( "de_DE.utf8" ); // I also tried this
        std::wcout.imbue ( loc );
        std::wcout << std::toupper<wchar_t> ( L't', loc ) << L'\n';
        std::wcout << std::use_facet< std::ctype<wchar_t> >(loc).toupper
( L't' ) << L'\n';
        std::wcout << std::toupper<wchar_t> ( L'ä', loc ) << L'\n';
        std::wcout << std::use_facet< std::ctype<wchar_t> >(loc).toupper
( L'ä' ) << L'\n';
        return 0;

}

Please note that I really want to use standard c++ for solving the problem.

Many thanks in advance,
Kay