Binary Search Tree- deleting a node causes other methods errors c++ - c++

Question

I have a problem with deleting node from BST. I wrote a method that searches a node, that works fine, and when I'm trying to delete a leaf (an only case that I wrote so far) it causes an error (0xDDDD...) in printing methods. I assume that is because printing methods encounter some kind of null, but I have no idea how to fix that. Here is the code...
Deleting node by value method:
void deleteNodeByValue(T val)
{
cout << "\nElement to delete: " << val << " \n";
Node<T>* tmp = root;
while (tmp != NULL)
{
if (val == tmp->data)
{
cout << "Element found: " << tmp->data << " \n";
if (tmp->right_child == NULL && tmp->left_child == NULL)
{
delete tmp;
tmp = NULL;
size--;
}
break;
}
else if (val > tmp->data)
{
tmp = tmp->right_child;
}
else if (val < root->data)
{
tmp = tmp->left_child;
}
}
}
and tree print:
string to_string()
{
stringstream ss;
Node<T>* tmp = root;
queue<Node<T>*> q;
while (!q.empty() || tmp != NULL)
{
if (tmp != NULL)
{
q.push(tmp);
tmp = tmp->left_child; //debugger shows error in this place
}
else
{
tmp = q.front();
q.pop();
ss << "Data: " << tmp->data;
if (tmp->left_child != NULL)
{
ss << " Left child: " << tmp->left_child->data;
}
if (tmp->right_child != NULL)
{
ss << " Right child: " << tmp->right_child->data;
}
ss << " \n";
tmp = tmp->right_child;
}
}
return ss.str();
It also causes error in other methods like getting tree height or getting trees in order, whatever.
What should I do?

Answer 1

Simple, you delete the node, but the parent of that node still points to it. So you are trying to print a deleted node.
You have to remember who was the parent of the node you delete and to update it to no longer point to it.
Many ways to do it, I personally would make tmp a double pointer if I was you but since your name is newbie here is a little easier to read solution:
cout << "\nElement to delete: " << val << " \n";
Node<T>* tmp = root;
Node<T>* parent = NULL;
while (tmp != NULL)
{
if (val == tmp->data)
{
cout << "Element found: " << tmp->data << " \n";
if (tmp->right_child == NULL && tmp->left_child == NULL)
{
if (parent == NULL) root = NULL;
else {
if (parent->right_child == tmp) {
parent->right_child = NULL;
} else {
parent->left_child = NULL;
}
}
delete tmp;
size--;
}
break;
}
else if (val > tmp->data)
{
parent = tmp;
tmp = tmp->right_child;
}
else if (val < root->data)
{
parent = tmp;
tmp = tmp->left_child;
}
}
Of course you have to add the handling for the case when node is not a leaf too, but it looks like you understand this.