std::basic_ios<CharT,Traits>::swap (3) - Linux Man Pages
protected: (since C++11)
void swap( basic_ios& other ) noexcept;
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.
other - the basic_ios object to exchange the state with
move moves from another std::basic_ios except for rdbuf