std::swap(std::shared_ptr)(3)

NAME
std::swap(std::shared_ptr) - std::swap(std::shared_ptr)

Synopsis
   Defined in header <memory>
   template< class T >
   void swap( std::shared_ptr<T>& lhs, std::shared_ptr<T>& rhs ) (since C++11)
   noexcept;
   Specializes the std::swap algorithm for std::shared_ptr. Swaps the contents of lhs
   and rhs. Calls lhs.swap(rhs).

Parameters
   lhs, rhs - smart pointers whose contents to swap

Return value
   (none)

Complexity
   Constant.

Example
// Run this code
 #include <iostream>
 #include <memory>
 #include <string>
 struct Foo {
     Foo(int _val) : val(_val) { std::cout << "Foo...\n"; }
     ~Foo() { std::cout << "~Foo...\n"; }
     std::string print() { return std::to_string(val); }
     int val;
 };
 int main()
 {
     std::shared_ptr<Foo> p1 = std::make_shared<Foo>(100);
     std::shared_ptr<Foo> p2 = std::make_shared<Foo>(200);
     auto print = [&]() {
         std::cout << " p1=" << (p1 ? p1->print() : "nullptr");
         std::cout << " p2=" << (p2 ? p2->print() : "nullptr") << '\n';
     };
     print();
     std::swap(p1, p2);
     print();
     p1.reset();
     print();
     std::swap(p1, p2);
     print();
 }

Output:
 Foo...
 Foo...
  p1=100 p2=200
  p1=200 p2=100
 ~Foo...
  p1=nullptr p2=100
  p1=100 p2=nullptr
 ~Foo...

See also
   swap swaps the values of two objects
        (function template)
   swap swaps the contents
        (public member function)