Effects: Constructs an object of class basic_istream, assigning initial values to the base class by calling basic_ios::init(sb) ([basic.ios.cons]).
Postcondition: gcount() == 0
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.
Effects: Destroys an object of class basic_istream.
Remarks: Does not perform any operations of rdbuf().