Question

I have to implement a binary search tree using C++ for one of assignments. I’ve created the class, and attempted to implement the InsertItem, PrintTree, DeleteTree methods for the class, I think I did everything right but for some reason my program keeps crashing 🙁

Here’s my code:

PrintTree Method

template <class TItem>
void BinarySearchTree<TItem>::PrintTree()
{
    PrintTree(RootNode);
}

template <class TItem>
void BinarySearchTree<TItem>::PrintTree(BinarySearchTreeNode* Node)
{
    if(Node == NULL)
        return;

    cout << Node->Data << endl;
    PrintTree(Node->LeftChild);
    PrintTree(Node->RightChild);
}

DeleteTree Method

template <class TItem>
void BinarySearchTree<TItem>::DeleteTree()
{
    DeleteTree(RootNode);
}

template <class TItem>
void BinarySearchTree<TItem>::DeleteTree(BinarySearchTreeNode* Node)
{
    if(Node == NULL)
        return;

    DeleteTree(Node->LeftChild);
    DeleteTree(Node->RightChild);

    delete Node;
}

My sequence of method calls up until the program crashes:

I insert items F,B,G,A,D,I,C,E,H: works fine

I call PrintTree(): works fine

I call DeleteTree(): works fine

I call PrintTree() again: program crashes

For some reason the expression if(RootNode == NULL) is not returning true after the DeleteTree() method is called, so the program tries to print something that doesn’t exist and crashes. I’m not sure why this is happening, what am I doing wrong here?

Any and all help is appreciated.

Answer 1

Calling “delete” does not null out the pointer.
You will want to do:

delete Node; 
Node = nullptr;

EDIT:

Pass the pointer by address so that you can clean up dangling pointers as you go:

void BinarySearchTree<TItem>::DeleteTree(BinarySearchTreeNode *&node);