std::basic_ostream<CharT,Traits>* tie() const; (1) std::basic_ostream<CharT,Traits>* tie( std::basic_ostream<CharT,Traits>* str ); (2)
Manages the tied stream. A tied stream is an output stream which is synchronized with the sequence controlled by the stream buffer (rdbuf()), that is, flush() is called on the tied stream before any input/output operation on *this.
1) Returns the current tied stream. If there is no tied stream, NULL is returned.
2) Sets the curr