When you have a class with a pointer as a data member, presumably objects
you instantiate of that class will have dynamic memory (new operator).

All classes whose objects will have dynamic memory MUST have:

1. copy constructor
2. overloaded assignment operator
3. destructor

If you don't want to allow copying of your object, you can make the copy
and operator= private.

If you do not write a copy and operator=, the default for these (which does a
memberwise copy) will be used.  This makes a shallow copy. This means two
objects share memory, generally not what you want.

You want to make a deep copy so all objects own their own memory.