explicit basic_stringstream(ios_base::openmode mode = ios_base::in | ios_base::out);
explicit basic_stringstream(const basic_string<E, T, A>& x,
ios_base::openmode mode = ios_base::in | ios_base::out);The first constructor initializes the base class by calling basic_iostream(sb), where sb is the stored object of class
basic_stringbuf<E, T, A>. It also initializes sb by calling basic_stringbuf<E, T, A>(mode).
The second constructor initializes the base class by calling basic_ostream(sb). It also initializes sb by calling
basic_stringbuf<E, T, A>(x, mode).