Causes output to be buffered and processed on when the buffer is full.
A reference to an object of type ios_base, or to a type that inherits from ios_base.
A reference to the object from which _Str is derived.
unitbuf causes the buffer to be processed when it is not empty.
The manipulator effectively calls _Str.unsetf(ios_base::unitbuf), and then returns _Str.