state_type state() const;
streambuf* rdbuf() const;
streambuf* rdbuf(streambuf* bytebuf);
using state_type = typename Codecvt::state_type;
explicit wbuffer_convert(
streambuf* bytebuf,
Codecvt* pcvt = new Codecvt,
state_type state = state_type());
~wbuffer_convert();