C ++二叉树，修改根节点，指向根节点的指针

Question

I realize the title isn't too descriptive so here are the details. I'm implementing my own Binary Tree class in C++. I have written a template Node class and template Binary Tree class already, for the most part, and am stuck on something. I created an empty binary tree (root node is null) and when I try to set that node it fails miserably. here is the code and more explanation:

template<class T> class Node
{
    T _key;
    Node<T> *_leftChild;
    Node<T> *_rightChild;

    public:
        Node();
        Node(T key);
        Node(T key, Node<T> *leftChild, Node<T> *rightChild);
        ~Node();

        bool hasLeftChild();
        bool hasRightChild();

        void setKey(T key);
        void setLeftChild(Node<T> *node);
        void setRightChild(Node<T> *node);

        T getKey();
        Node<T>* getLeftChild();
        Node<T>* getRightChild();

        bool compare(Node<T> *compareNode); // return true if this.Node < compareNode
};

Node implementation not really necessary.. ( I dont think ) it's quite long.

#include "Node.cpp"
#include <iostream>
using namespace std;

template<class T> class BinaryTree
{
    Node<T> *_root;

    public:
        BinaryTree();
        BinaryTree(Node<T> *root);
        ~BinaryTree();

        Node<T>* getRoot();
        void insert(Node<T> **root, Node<T> *node);
};

template<class T>
BinaryTree<T>::BinaryTree()
{
    this->_root = NULL;
}

template<class T>
BinaryTree<T>::BinaryTree(Node<T> *root)
{
    this->_root = root;
}

template<class T>
BinaryTree<T>::~BinaryTree()
{
    // delete stuff
}

template<class T>
Node<T>* BinaryTree<T>::getRoot()
{
    return this->_root;
}

template<class T>
void BinaryTree<T>::insert(Node<T> **root, Node<T> *node)
{
    if(!*root)
    {
        *root = node;
    }
}

Main:

BinaryTree<int> *tree = new BinaryTree<int>();

Node<int> *root = tree->getRoot();
Node<int> **root1 = &root;

cout << tree->getRoot() << endl;
Node<int> *noChildrenNode = new Node<int>(2);
tree->insert(&root1, noChildrenNode);
cout << tree->getRoot() << endl;

Inserts current functionality is just supposed to replace the NULL root pointer to the node pointer passed in as a parameter. The failing miserably part is since the pointer is a copy it isn't actually setting the root node.. but I can't seem to figure out how to set up a pointer to a pointer to the root node so it can be altered.. I've got to be close and any help will be MUCH appreciated.

Thanks

Answer 1

First, you've got to include the exact text of any error messages. "fails miserably" is not adequate.

I think you want

 root = node;

Not

 *root = node;

Because if root is null, using *root is a null pointer exception.