#include <ostream>
template<typename ch = char, typename tr = std::char_traits<ch> >
class buffer : public std::basic_streambuf<ch, tr> {
    virtual
    int_type    overflow(int_type c = tr::eof());

    virtual
    typename int_type   overflow1(typename int_type c = tr::eof());

    using std::basic_streambuf<ch, tr>::int_type;

    virtual
    int_type    overflow2(int_type c = tr::eof());

    virtual
    typename int_type   overflow3(typename int_type c = tr::eof());

    virtual
    std::basic_streambuf<ch, tr>::int_type  overflow4(
        std::basic_streambuf<ch, tr>::int_type c = tr::eof());

    virtual
    typename std::basic_streambuf<ch, tr>::int_type overflow5(
        typename std::basic_streambuf<ch, tr>::int_type c = tr::eof());
    };
int main() {
    buffer<> b;
    }

gets you:

~/ootbc/common/test/src$ g++ foo.cc
foo.cc:5: error: `int_type' does not name a type
foo.cc:5: error: (perhaps `typename std::basic_streambuf<_CharT,
_Traits>::int_type' was intended)
foo.cc:8: error: expected nested-name-specifier before "int_type"
foo.cc:8: error: `int_type' does not name a type
foo.cc:8: error: (perhaps `typename std::basic_streambuf<_CharT,
_Traits>::int_type' was intended)
foo.cc:13: error: `int_type' does not name a type
foo.cc:13: error: (perhaps `typename std::basic_streambuf<_CharT,
_Traits>::int_type' was intended)
foo.cc:16: error: expected nested-name-specifier before "int_type"
foo.cc:16: error: `int_type' does not name a type
foo.cc:16: error: (perhaps `typename std::basic_streambuf<_CharT,
_Traits>::int_type' was intended)
foo.cc:19: error: ISO C++ forbids declaration of `int_type' with no type
foo.cc:19: error: cannot declare member `std::basic_streambuf<_CharT,
_Traits>::int_type' within `buffer<ch, tr>'
foo.cc:19: error: expected `;' before "overflow4"


As suggested in the error for "overflow" (good message BTW), the form used in 
"overflow5" works. But a "using" for the inherited name "int_type" does not make 
the name visible either directly (overflow2) or when tagged with "typename" 
(overflow 3). But the "using" doesn't complain either. If I can "using" it I 
should be able to "use" it :-)

Ivan