That's hard to say without seeing the code for it.
I haven't written the code/implementation yet because the destructor gives me the error of "invalid destructor declaration" .
The name of the destructor must exactly match the name of the class (with the ~ in front of course).
Line 14, your class name is DoublyLinkedList_h (with _h), while on line 19 your destructor is DoublyLinkedList (no _h), so the compiler is trying to tell you they don't match,
Also, if line 17 and 18 are supposed to be constructors, constructors don't have a return type.
Makes perfect sense. Thank you !