如何创建一个过去的迭代器？

Question

I have created a binary tree structure to store a bounded volume hierarchy, to make it easier to use (and safer) I created two iterators to complement it: breadth-first and depth-first.

The breadth-first iterator is essentially a wrapper for the underlying QList. But I am stuck on the depth-first iterator (bidirectional only), I can handle the actual iteration around the tree, I just do not how to create a past-the-end iterator.

I can't just use the QList::end() because there is no guarantee the lowest-level rightmost node is also the rightmost node of the whole tree. I'm reluctant to make a 'fake' BVH node that can tested for because it will involve a large code change (and probably overhead) to have the various node management mechanisms ignore the fake node, and disable a lot of the tree building automation (for example the parent of the fake node will have to be told it is a leaf). But if this is the only way - then it is the only way.

Answer 1

Having looked briefly at qlist.h, it appears that you won't be able to use the same end() for both iteration types. But that's OK--you can use a null pointer or a static dummy or other techniques to make an end() iterator for your second iteration method. I don't see why this would have to impact a huge amount of other code (most of which should just refer to end() without knowing its implementation details).

Answer 2

Can you not just use null or something like this as end? This is at least what I would expect eg for a linked list structure.