void swap( basic_ios& other );
Exchanges the states of *this and
other, except for the associated
rdbuf objects. rdbuf() and other.rdbuf() returns the same values as before the call.
This swap function is protected: it is called by the swap member functions of the derived stream classes such as std::basic_ofstream or std::basic_istringstream, which know how to correctly swap the associated streambuffers.
 Return value
 See also
| moves from another std::basic_ios except for
(protected member function)