Question

I’ve been told that when if I have multiple pointers pointing to the same object, I cannot delete it normally (using the delete keyword). Instead, I’ve been told that I need to set the pointers to NULL or 0.

Given I have:

ClassA* object = new ClassA();
ClassA* pointer1 = object;
ClassA* pointer2 = object;

So to delete pointer1 and pointer2, do I need to do the following?

pointer1 = 0;
pointer2 = 0:

Once I’ve set it to NULL, do I still need to use the keyword delete? Or is just setting it to 0 good enough?

Answer 1

Whenever you new an object, you need to delete it, free’ing the memory

ClassA* object = new ClassA();

delete object; // Free's the memory you allocated.

The point of setting your pointers to NULL is to stop dereferencing pointers that are invalid

object = NULL;

This is done so that tests can be performed before attempting a dereference:

if(object != NULL)
{
  object->SomeMethod(); // We can assume it's safe to use the pointer.
}

Also note that you can delete the memory from any pointer that points to it.

ClassA* object = new ClassA();
ClassA* pointer1 = object;
ClassA* pointer2 = object;

delete pointer1; 

object, pointer1, and pointer2 now all point to memory that has already been released, and unless they will be redefined, they should all be set to NULL.