How can I determine if a C++ object has been deallocated?

Question

I have a previous question that was answered in which I describe difficulties catching an exception when I try to access an object that has been deallocated by a third-party

Answer 1

You can't easily tell just by looking at the memory location if the object is still allocated or not. There might be some black magic tricks to do that, but a much cleaner way would be to build a call-back mechanism into the object's destructor.