std::basic_ostream::swap(3)

NAME
std::basic_ostream::swap - std::basic_ostream::swap

Synopsis
   protected: (since C++11)
   void swap( basic_ostream& rhs );
   Calls basic_ios::swap(rhs) to swap all data members of the base class, except for
   rdbuf(), between *this and rhs. This swap function is protected: it is called by the
   swap functions of the swappable output stream classes std::basic_ofstream and
   std::basic_ostringstream, which know how to correctly swap the associated
   streambuffers.

Parameters
   rhs - a basic_ostream of the same type to swap with

Example
// Run this code
 #include <iostream>
 #include <sstream>
 #include <utility>
 int main()
 {
     std::ostringstream s1("hello");
     std::ostringstream s2("bye");
     s1.swap(s2); // OK, ostringstream has a public swap()
     std::swap(s1, s2); // OK, calls s1.swap(s2)
 // std::cout.swap(s2); // ERROR: swap is a protected member
     std::cout << s1.str() << '\n';
 }

Output:
 hello