Question

I have an object say.

ClassA *obj1 = new ClassA;

ClassA *ptr1 = obj1;
ClassA *ptr2 = obj1;

When I do delete ptr1;, will it affect ptr2? If so what can be the correct solution for this?

Answer 1

(assuming obj2 is supposed to be obj1)

ClassA *x defines a pointer that can point to objects of type ClassA. A pointer isn’t an object itself.

new ClassA allocates (and constructs) an actual object of type ClassA.

So the line Class A *obj1 = new ClassA; defines a pointer obj1 and then sets it to point to a newly allocated object of type ClassA.

The line Class A *ptr1 = obj1; defines a pointer ptr1 and then sets it to point to the same thing obj1 is pointing to, that is, the ClassA object we just created.

After the line Class A *ptr2 = obj1;, we have three pointers (obj1, ptr1, ptr2) all pointing to the same object.

If we do delete ptr1; (or equivalently, delete obj1; or delete ptr2;), we destroy the pointed to object. After doing this, any pointer that was pointing to the object is made invalid (which answers your first question: yes, it will affect ptr2 in the sense that ptr2 won’t be pointing to a valid object afterwards).

The correct solution depends on what you’re trying to achieve:

• If you want two copies of the object, assuming ClassA has a copy constructor, do ClassA *ptr2 = new ClassA(*obj1);. You will need to delete this new object separately when you are done with it!
• If you want two pointers to the same object, consider using something like boost::shared_ptr (google it)

Hmm, that’s alot of text for such a simple q+a. Ah well.