std::swap(std::unique_ptr)

Defined in header <memory>.

Declarations

C++11

template< class T, class D >
void swap( std::unique_ptr<T, D>& lhs, std::unique_ptr<T, D>& rhs ) noexcept;

C++23

template< class T, class D >
constexpr void swap( std::unique_ptr<T, D>& lhs, std::unique_ptr<T, D>& rhs ) noexcept;

Specializes the std::swap algorithm for std::unique_ptr. Swaps the contents of lhs and rhs. Calls lhs.swap(rhs).

This function does not participate in overload resolution unless std::is_swappable_v<D> is true(since C++17).

Parameters

lhs, rhs - smart pointers whose contents to swap

Return value

(none)

Complexity

Constant

Example

#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::unique_ptr<Foo> p1 = std::make_unique<Foo>(100);
    std::unique_ptr<Foo> p2 = std::make_unique<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();   
}

Result

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