std::swap (非メンバ関数)(C++11)

#include <iostream>
#include <memory>

int main()
{
  std::shared_ptr<int> sp1(new int(1));
  std::weak_ptr<int> wp1 = sp1;

  std::shared_ptr<int> sp2(new int(2));
  std::weak_ptr<int> wp2 = sp2;

  if (std::shared_ptr<int> r = wp1.lock()) {
    std::cout << r << std::endl;
  }

  if (std::shared_ptr<int> r = wp2.lock()) {
    std::cout << r << std::endl;
  }

  // wp1とwp2を入れ替える
  std::swap(wp1, wp2);

  if (std::shared_ptr<int> r = wp1.lock()) {
    std::cout << r << std::endl;
  }

  if (std::shared_ptr<int> r = wp2.lock()) {
    std::cout << r << std::endl;
  }
}