C++ virtual function table memory cost

Question

Consider:

class A
{
    public:
        virtual void update() = 0;
}

class B : public A
{
    public:
        void update() { /* stuff goes in here... */ }
         


        

Answer 1

Moving away from the non issue of the vtable pointer in your object:

Your code has other problems:

A * array = new A[1000];
array[0] = new B();
array[1] = new C();

The problem you are having is the slicing problem.
You can not put an object of class B into a space the size reserved for an object of class A.
You will just slice the B(or C) part of the object clean off leaving you with just the A part.

What you want to do. Is have an array of A pointers so that it hold each item by pointer.

A** array = new A*[1000];
array[0]  = new B();
array[1]  = new C();

Now you have another problem of destruction. Ok. This could go on for ages.
Short answer use boost:ptr_vector<>

boost:ptr_vector  array(1000);
array[0] = new B();
array[1] = new C();

Never allocte array like that unless you have to (Its too Java Like to be useful).