NAME

std::weak_ptr::~weak_ptr - std::weak_ptr::~weak_ptr

Synopsis

~weak_ptr(); (since C++11)

Destroys the weak_ptr object. Results in no effect to the managed object.

Example

The program shows the effect of "non-breaking" the cycle of std::shared_ptrs.

// Run this code

#include <iostream>
#include <memory>
#include <variant>

class Node {
char id;
std::variant<std::weak_ptr<Node>, std::shared_ptr<Node>> ptr;
public:
Node(char id) : id{id} {}
~Node() { std::cout << " '" << id << "' reclaimed\n"; }
/*...*/
void assign(std::weak_ptr<Node> p) { ptr = p; }
void assign(std::shared_ptr<Node> p) { ptr = p; }
};

enum class shared { all, some };

void test_cyclic_graph(const shared x) {

auto A = std::make_shared<Node>('A');
auto B = std::make_shared<Node>('B');
auto C = std::make_shared<Node>('C');

A->assign(B);
B->assign(C);

if (shared::all == x) {
C->assign(A);
std::cout << "All links are shared pointers";
} else {
C->assign(std::weak_ptr<Node>(A));
std::cout << "One link is a weak_ptr";
}
/*...*/
std::cout << "\nLeaving...\n";
}

int main() {
test_cyclic_graph(shared::some);
test_cyclic_graph(shared::all); // produces a memory leak
}

Output:

One link is a weak_ptr
Leaving...
'A' reclaimed
'B' reclaimed
'C' reclaimed
All links are shared pointers
Leaving...

See also

destructor destructs the owned object if no more shared_ptrs link to it
(public member function of std::shared_ptr<T>)