explicit basic_istream(basic_streambuf<charT, traits>* sb);
Effects: Constructs an object of class basic_istream, initializing the base class subobject with basic_ios::init(sb) ([basic.ios.cons]).
basic_istream(basic_istream&& rhs);
Effects: Move constructs from the rvalue rhs. This is accomplished by default constructing the base class, copying the gcount() from rhs, calling basic_ios<charT, traits>::move(rhs) to initialize the base class, and setting the gcount() for rhs to 0.
virtual ~basic_istream();