23 template<typename Ch, typename Mode>
26     typedef Ch char_type;
32     std::streamsize read(Ch*, std::streamsize) { return -1; }  in read()  argument
33     std::streamsize write(const Ch*, std::streamsize n) { return n; }  in write()  argument
42 template<typename Ch>
43 struct basic_null_source : private basic_null_device<Ch, input> {
44     typedef Ch          char_type;
46     using basic_null_device<Ch, input>::read;
47     using basic_null_device<Ch, input>::close;
53 template<typename Ch>
54 struct basic_null_sink : private basic_null_device<Ch, output> {
55     typedef Ch        char_type;
57     using basic_null_device<Ch, output>::write;
58     using basic_null_device<Ch, output>::close;