Question

I have a doubt, the function below can receive an object of type A or something derived type.

A *copyToHeap(A &obj) {
    A *ptr=new A(obj);
    return ptr;
}

If we call it like this:

//B inherits from A
B bObj;
B *hPtr=copyToHeap(bObj);

The object pointed by hPtr is actually of type A or B?
Is safe doing this?

Answer 1

when you do the below in your code:

A* ptr = new A(obj);

you’ll always get an A instance. obj will be treated as an A and a new A will get created based on the “A part” of obj.

The better approach is as an earlier reply indicated, add a virtual MakeCopy method to the base class and implement it for the derived classes.

virtual A* MakeCopy();

This method is implemented by making a copy of the object for which its called. It then gets implemented in the derived classes so if you have an A pointer which is actually a B object you’ll get a true B copy and avoid the “slicing” which is occurring in your example.