making a copy of a list of pointers to objects

[theDuke]

Hello,

i just wanted to ask what the best way would be to make a copy of a list of pointers to objects. The objects themselves each contain more pointers to other objects. All of these pointers should point to new objects in the copied list and not to the original objects.

I thought it might be good to write a copy constructor for the list but I'm not sure how I would do that. Do I have to use inheritance?

Any help would be appreciated.

Thanks.

[Ganon11]

You should not need inheritance.

What you are saying is you have 1 linked list (list1) containing pointers to objects. You want to create a new list (list2) containing pointers to objects. Each object of list2 should have the same properties as the objects of list1, but they should be separate objects - as well, the pointers of list2 will be pointing to different locations then list1.

You will need to access a node of list1. You will have access to its data (the pointer) and the next node. You should get the object that the data points to, create a pointer to that object type and initialize it to a new object (passing the list1 object as a parameter), then add the new pointer to list2. Then you can repeat on the next node.

You will have to write your own copy constructor for the class.

[theDuke]

Thanks Ganon11 for the prompt reply. Your description of what I want to do is exactly right yes. And I can see how your proposed solution would work. I just thought it would be nice to be able to say something like list<ObjectType *> list2 = getCopyOfList(); and then getCopyOfList() has at the end return list1; and then by using copy constructors, it would automatically make a complete new copy of the list.

It would look really clean and if I'm not mistaken, it would also mean that when the function from which I call list< ObjectType *> list2 = getCopyOfList() exits, the destructor of list2 would automatically be called and I could make it delete all the objects being pointed at in the list by overloading the destructor of the list... I don't know if that is clear enough, it seems a bit complex :o)

[Ganon11]

That's clear, but from a short description like that, it sounds like getCopyOfList would create a shallow copy. That is, the new list you create would have new pointers, but these pointers would point to the same objects as in list1. This is why you have to be especially careful when copying pointers - you don't want to end up with 2 pointers pointing to 1 object.