std::basic_istream::swap

From cppreference.com
< cpplrm; | iolrm; | basic istream
protected:
void swap(basic_istream& rhs);
(since C++11)

Calls basic_ios::swap(rhs) to swap all data members of the base class except for rdbuf(), and swaps the values of the gcount() counters between *this and rhs. This swap function is protected: it is called by the swap functions of the swappable input stream classes std::basic_ifstream and std::basic_istringstream, which know how to correctly swap the associated streambuffers.

Parameters

rhs - different basic_istream object of the same type to swap with

Example

#include <sstream>
#include <iostream>
#include <utility>
int main()
{
    std::istringstream s1("hello");
    std::istringstream s2("bye");

    s1.swap(s2); // OK, istringstream has a public swap()
    std::swap(s1, s2); // OK, calls s1.swap(s2)
//  std::cin.swap(s2); // ERROR: swap is a protected member

    std::cout << s1.rdbuf();
}

Output:

hello