std::weak_ptr

weak_ptr_example.cpp

#include <iostream>
#include <memory>
 
std::weak_ptr<int> gw;
 
void f()
{
    // Has to be copied into a shared_ptr before usage
    if (auto spt = gw.lock()) {
        std::cout << *spt << "\n";
    }
    else {
        std::cout << "gw is expired\n";
    }
}
 
int main()
{
    {
        auto sp = std::make_shared<int>(42);
        gw = sp;
        
        f(); // 42
    }

    f(); // gw is expired
}