Question

Although this is a very general question, here’s my specific example so you can understand what I’m asking.

I have a copy constructor for a quad-tree class. So I write a recursive helper method called copy so I can call it in my copy constructor. The helper takes one parameter, a node. The root node is given as the first argument when called from the constructor.

So now in my helper method, I create one new node call it newNode, and each node has member variables neChild, nwChild, seChild, swChild—-sw means southwest nw, ne, se are all cardinal directions, and I set each new child equal to that of source.child. Then I call the helper method again recursively on each source.child (4 of them). So this way, 1 node becomes 4, which then has 16 childs, and so on. And so then I return that first newNode I created.

Question:

Will that new returned node have all the other nodes attached to it? Will it be in a tree structure (although not formally a tree)? Or will those pointers attached to returned pointers go out of scope?

Answer 1

You will end up with a new root node which is linked to the same child nodes as the original tree. So any changes made to any children will affect both trees, and you may have a double-free problem later.

This is because, although you’re calling copy recursively, you’re discarding the return value.

Furthermore, you said this copy function is called from your copy constructor? You’re in for a world of hurt, because copy calls the copy constructor (at the return statement, since you return by value). That’s a recipe for a STACK OVERFLOW. I guess you’re in the right place 😉