NAME¶

std::weak_ptr::swap - std::weak_ptr::swap

Synopsis¶

void swap( weak_ptr& r ) noexcept; (since C++11)

Exchanges the stored pointer values and the ownerships of *this and r. Reference
counts, if any, are not adjusted.

Parameters¶

r - smart pointer to exchange the contents with

Return value¶

(none)

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> sp1 = std::make_shared<Foo>(100);
std::shared_ptr<Foo> sp2 = std::make_shared<Foo>(200);
std::weak_ptr<Foo> wp1 = sp1;
std::weak_ptr<Foo> wp2 = sp2;
auto print = [&]() {
auto p1 = wp1.lock();
auto p2 = wp2.lock();
std::cout << " p1=" << (p1 ? p1->print() : "nullptr");
std::cout << " p2=" << (p2 ? p2->print() : "nullptr") << '\n';
};
print();

wp1.swap(wp2);
print();

wp1.reset();
print();

wp1.swap(wp2);
print();
}

Output:¶

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