basic_ostringstream& operator=(basic_ostringstream&& rhs);
void swap(basic_ostringstream& rhs);
Effects: Меняет состояние *this и rhs по вызову basic_ostream<charT, traits>::swap(rhs) и sb.swap(rhs.sb).
template <class charT, class traits, class Allocator>
void swap(basic_ostringstream<charT, traits, Allocator>& x,
basic_ostringstream<charT, traits, Allocator>& y);