Binary Search Tree Forgetting Every Node I Add

Question

My problem is seemingly simple, but I can't find its solution. I have a binary tree, and this is my add function:

void collection::addToTree(vendor *& item)
{
    Node * curr = root;
    while (curr)
    {
        if (strcmp(item->getName(), root->item->getName()) < 0)
            curr = curr->left;
        else
            curr = curr->right;
    }
    curr = new Node(item);
}

And this is my Node constructor:

collection::Node::Node(vendor *& item) : left(nullptr), right(nullptr)
{
    this->item = item;
}

However, the tree is always empty, no matter what or how many items I try to add to it. The only other piece of code I can think of that will help you guys is my struct for my tree:

struct Node
{
    Node();
    Node(vendor *& item);
    vendor * item;
    Node *left, *right;
};
Node * root;

All of the sub-variables of vendor do have values (as I've seen in my debugger). I wish I could give you guys more detail, but this is all I know about the error. Any feedback is greatly appreciated.

Answer 1

在add函数中，您仅使curr指向新项，但这并不会变回先前的左/右指针，这可能正是您的目标。

Answer 2

You need to modify the left/right pointers directly, something like this:

void collection::addToTree(vendor *& item)
{
    Node * curr = root;
    while (curr)
    {
        if (strcmp(item->getName(), curr->item->getName()) < 0)
        {
            if (!curr->left)
            {
                curr->left = new Node(item);
                return;
            }
            curr = curr->left;
        }
        else
        {
            if (!curr->right)
            {
                curr->right = new Node(item);
                return;
            }
            curr = curr->right;
        }
    }
    root = new Node(item);
}

Also, make sure you do Node * root = nullptr , as no initializing it can lead to it containing any arbitrary value.

Notice that I also changed if (strcmp(item->getName(), root->item->getName()) < 0) to if (strcmp(item->getName(), curr->item->getName()) < 0) , as the branching is dependent on curr , not root .

Answer 3

I think the problem here is that your curr variable should be declared as Node **curr and receive the root's address in order for the change to be visible outside of the addToTree function.

void collection::addToTree(vendor *& item)
{
    Node ** curr = &root;
    while (*curr)
    {
        if (strcmp(item->getName(), (*curr)->item->getName()) < 0)
            (*curr) = (*curr)->left;
        else
            (*curr) = (*curr)->right;
    }
    *curr = new Node(item);
}