+ size_t bufsize = m_o_streambuf->GetBufferEnd() - m_o_streambuf->GetBufferStart();
+ size_t oldpos = m_o_streambuf->GetIntPosition();
+ m_o_streambuf->Write(buffer, nbytes);
+ size_t newpos = m_o_streambuf->GetIntPosition();
+ if (newpos == 0) return bufsize - oldpos;
+ else return newpos - oldpos;