namespace std {
    template<class charT,
             class traits = char_traits<charT>,
             class Allocator = allocator<charT> >
    class basic_string;
}

namespace std {
    template<class charT,
             class traits = char_traits<charT> >
    class basic_istream;
    template<class charT,
             class traits = char_traits<charT> >
    class basic_ostream;
    ...
}