std::swap - cppreference.com

Exchanges the given values.

1) Constant.

2) Linear in N.

The expected way to make a program-defined type swappable is to provide a non-member function swap in the same namespace as the type: see Swappable for details.

specializes the std::swap algorithm
(function template) [edit] specializes the std::swap algorithm
(function template) [edit] specializes the std::swap algorithm
(function template) [edit] specializes the std::swap algorithm
(function template) [edit] specializes the std::swap algorithm
(function template) [edit] specializes the std::swap algorithm
(function template) [edit] specializes the std::swap algorithm
(function template) [edit] specializes the std::swap algorithm
(function template) [edit] specializes the std::swap algorithm
(function template) [edit] specializes the std::swap algorithm
(function template) [edit] specializes the std::swap algorithm
(function template) [edit] specializes the std::swap algorithm
(function template) [edit] specializes the std::swap algorithm
(function template) [edit] specializes the std::swap algorithm
(function template) [edit] specializes the std::swap algorithm
(function template) [edit] specializes the std::swap algorithm
(function template) [edit] specializes the std::swap algorithm
(function template) [edit] specializes the std::swap algorithm
(function template) [edit] specializes the std::swap algorithm
(function template) [edit] specializes the std::swap algorithm
(function template) [edit] specializes the std::swap algorithm
(function template) [edit] specializes the std::swap algorithm
(function template) [edit] specializes the std::swap algorithm
(function template) [edit] specializes the std::swap algorithm
(function template) [edit] specializes the std::swap algorithm
(function template) [edit] specializes the std::swap algorithm
(function template) [edit] specializes the std::swap algorithm
(function template) [edit] specializes the std::swap algorithm
(function template) [edit] specializes the std::swap algorithm
(function template) [edit] specializes the std::swap algorithm
(function template) [edit] specializes the std::swap algorithm
(function template) [edit] specializes the std::swap algorithm
(function template) [edit] specializes the std::swap algorithm
(function template) [edit] specializes the std::swap algorithm
(function template) [edit] specializes the std::swap algorithm
(function template) [edit] specializes the std::swap algorithm
(function template) [edit] specializes the std::swap algorithm
(function template) [edit] specializes the std::swap algorithm
(function template) [edit] specializes the std::swap algorithm
(function template) [edit] specializes the std::swap algorithm
(function) [edit] specializes the std::swap algorithm
(function template) [edit] specializes the std::swap algorithm
(function template) [edit] specializes the std::swap algorithm
(function template) [edit] specializes the std::swap algorithm
(function template) [edit] specializes the std::swap algorithm
(function template) [edit] specializes the std::swap algorithm
(function) [edit] specializes the std::swap algorithm
(function template) [edit] specializes the std::swap algorithm
(function template) [edit] specializes the std::swap algorithm
(function) [edit] specializes the std::swap algorithm
(function) [edit] specializes the std::swap algorithm
(function) [edit] specializes the std::swap algorithm
(function) [edit] specializes the std::swap algorithm
(function) [edit] specializes the std::swap algorithm
(function) [edit]

#include <algorithm>
#include <iostream>

namespace Ns
{
    class A
    {
        int id {};
        
        friend void swap(A& lhs, A& rhs)
        {
            std::cout << "swap(" << lhs << ", " << rhs << ")\n";
            std::swap(lhs.id, rhs.id);
        }
        
        friend std::ostream& operator<<(std::ostream& os, A const& a)
        {
            return os << "A::id=" << a.id;
        }
    
    public:
        A(int i) : id {i} {}
        A(A const&) = delete;
        A& operator = (A const&) = delete;
    };
}

int main()
{
    int a = 5, b = 3;
    std::cout << a << ' ' << b << '\n';
    std::swap(a, b);
    std::cout << a << ' ' << b << '\n';
    
    Ns::A p {6}, q {9};
    std::cout << p << ' ' << q << '\n';
//  std::swap(p, q); // error, type requirements are not satisfied
    swap(p, q);      // OK, ADL finds the appropriate friend `swap`
    std::cout << p << ' ' << q << '\n';
}

Output:

5 3
3 5
A::id=6 A::id=9
swap(A::id=6, A::id=9)
A::id=9 A::id=6

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.