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.
| r | - | smart pointer to exchange the contents with |
(none).
#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...
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https://en.cppreference.com/w/cpp/memory/weak_ptr/swap