Is there a smart pointer that is automatically nulled when its target is destroyed in C++

Question

I've found QPointer. Are there any others?

Answer 1

Boost - the weak_ptr has some nice features that make it safe to use, if you are also using shared_ptr. You keep a weak_ptr reference to an instance that is managed by shared_ptr lifetime. When you need to use the underlying instance, convert it to a shared_ptr instance using the constructor of the shared_ptr class, or the lock method. The operation will fail if the underlying instance was deleted. The use is thread safe in the same fashion as the shared_ptr class:

shared_ptr<int> p(new int(5));
weak_ptr<int> q(p);

// some time later

if(shared_ptr<int> r = q.lock())
{
    // use *r
}

Answer 2

"boost::weak_ptr" works really well with "boost::shared_ptr" (also available in tr1)