#include<iostream>
#include<memory>
#include<vector>

using namespace std;

struct Link {
    int value;
    //shared_ptr<Link> other;
    weak_ptr<Link> other;
    Link(int v) { value = v; }  
    ~Link() { cout << "~Link\n"; }
};
ostream & operator<<(ostream & os, const Link &s) {
//    os << "Link " << &s << " -> " << s.other.get() << " v=" << s.value << endl;
    os << "Link " << &s << " -> " << s.other.lock().get() << " v=" << s.value << endl;
    return os;
}

int main()
{
    int x;
    shared_ptr<Link> p1(new Link(100));
    shared_ptr<Link> p2(new Link(200));
    cout << *p1;
    cout << *p2;
    p1->other = p2;
    p2->other = p1;
    cout << *p1;
    cout << *p2;
    cout << p1.use_count() << endl;
    cout << p2.use_count() << endl;
  
    weak_ptr<int> wp;
    {        
         auto sp = make_shared<int>(123);
         wp = sp;
         cout << wp.lock().get();
         cout << " " << wp.use_count();
         cout << " " << *(wp.lock()) << endl;
    }
    cout << " " << wp.use_count() << endl;
    if (wp.expired()) cout << "expired\n";
    if (wp.lock() == nullptr) cout << "sp nullptr\n";

    return 0;
}