Say I have Class1 and Class2 and I want a shallow copy constructor for Class1. Class1 has a member variable, which is a pointer pointing to a Class2 instance. Also I have to be able to change the Class2 ptr is pointing at.

in header file:

class Class1
{
    Class2* ptr;
    ...
}

in source file:

Class1::Class1()
{
    ptr = new Class2();
}

......

Class2* Class1::Exchange(Class2* newClass2)
{
    Class2* temp;
    ptr = newClass2;
    return temp;
}

......

Now say

Class1 original;
Class1 shallowCopy(original);

Class2* newClass2 = new Class2();
Class2* oldClass2;

oldClass2 = orignal.Exchange(newClass2);
delete oldClass2;

now I want is associate original.ptr with shallowCopy.ptr, when I implement the shallow copy constructor, how do I make sure these two pointer always point at the same Class2? I mean in the class above, the oldClass2 is deleted, so ptr of shallowCopy is pointing at nothing. If I don't delete oldClass2, ptrs of original and shallowCopy are pointing at different Class2 instance.