Deleting Pointers

Question

I wanted to ask, is dynamically creating a pointer, and then changing a pointer address to something else still deleting the original allocated space?

for example:

int main()
{

int c = 50;
    // Memory leak
    int * q = new int;
    q = & c;
    delete q;
}

What exactly is getting deleted or happening?

Thanks!

Answer 1

What exactly is getting deleted or happening?

Memory leaking and undefined behaviour.

When you do q = & c; you are losing your only tracking of the memory allocated by new int. Noone keeps track of this for you, there is no garbage collector, it is simply lost and cannot be recovered.

When you then do delete q; (where q is assigned to &c) you are deleting memory that you didn't allocate, and worse you are deleting memory on the stack. Either of these will result in undefined behavior.

---

This is an excellent preface into why you should avoid using pointers in circumstances where you don't need them. In this case, there is no reason dynamically allocate your int. If you really need a pointer, use a c++11 smart pointer (or boost if you don't have c++11). There are increasingly rare cases where you really do need a raw c type pointer. You should read Effective Modern c++ Chapter 4 for excellent detail on this subject.