Question

This is supposed to traverse a BST and delete every node, including the root node. However, at the end, I get the message “root still has a left node.” Why aren’t all nodes deleted?

void deleteTree()
{   
    deleteNode(root);
    if(root->right)
        cout << "root still has a right node" << endl;
    if(root->left)
        cout << "root still has a left node" << endl;
    root = 0;

}   

void deleteNode(node *p) 
{   
    if(p->left) 
    {   
        deleteNode(p->left);
        p->left = 0;
    }   
    if(p->right) 
    {   
        deleteNode(p->right);
        p->right = 0;
    }   

    cout << "Deleting node containing " << p->data << endl;
    delete p;
}   

Answer 1

Your are deleting p at the end (root) and then trying to access its contents in deleteTree(), where root no longer points to allocated memory. The result is going to be undefined.