explicit basic_iostream( std::basic_streambuf<CharT,Traits>* sb );

basic_iostream( const basic_iostream& other ) = delete;

protected:
basic_iostream( basic_iostream&& other );

1) Initializes with streambuf sb. The base classes are initialized as basic_istream<CharT,Traits>(sb) and basic_ostream<CharT,Traits>(sb). After the call rdbuf() == sb and gcount() == 0.

2) Copy construction is not allowed.

3) Move constructor: move-constructs the first base class basic_istream as basic_istream<CharT,Traits>(std::move(rhs));, which in turn move-constructs and initializes the virtual base std::basic_ios. The initialization of the other base, basic_ostream, is implementation-defined (e.g., a protected default constructor may be added to std::basic_ostream, which does nothing) because move-construction cannot use rhs twice. This move constructor is protected: it is called by the move constructors of the derived stream classes std::basic_fstream and std::basic_stringstream before they move-construct and associate the stream buffer.