std::weak_ptr<T>::swap
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std::weak_ptr
Member functions
Modifiers
weak_ptr::swap
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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.
[edit] Parameters
r
-
smart pointer to exchange the contents with
[edit] Return value
(none)
[edit] 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...