Question

Class A
{
  public:
    NullIt()
    {
      this = NULL;
    }

    Foo()
    {
      NullIt();
    }
}

A * a = new A;
a->Foo();

assert(a);  //should assert here

Is there a way to achieve this effect, memory leaks aside?

Answer 1

No. The object knows nothing about the external references to it (in this case, “a”), so it can’t change them.

If you want the caller to forget your object, then you can do this:

class MyClass
{
    void Release(MyClass **ppObject)
    {
        assert(*pObject == this);   // Ensure the pointer passed in points at us
        *ppObject = NULL;           // Clear the caller's pointer
    }
}


MyClass *pA = new A;
pA->Release(&pA);
assert(pA);               // This assert will fire, as pA is now NULL

When you call Release, you pass in the pointer you hold to the object, and it NULLs it out so that after the call, your pointer is NULL.

(Release() can also “delete this;” so that it destroys itself at the same time)