Tree class root node not updating

Question

I'm trying to write an AVL Tree class in C++ and im starting by just writing code for a normal BST but I have a problem. The problem I'm having is with my insert function. I try to insert elements into the tree it doesn't seem to actually do it. I'm not quite sure why it isn't doing so, my hunch is that I'm changing the tree from within the functions but I don't do anything to save those changes and I don't know how to go about doing that.

#ifndef AVLTREE_H
#define AVLTREE_H
#include <iostream>

template <class K, class V>
struct AVLNode{
    K Key;
    V Value;
    AVLNode<K,V> *left;
    AVLNode<K,V> *right;
};

template <class K, class V>
class AVLTree{
    public:
        AVLTree();
        ~AVLTree();
        void insert(const K& Key, const V& Value);
        void print_AVL();
    private:
        void print_AVL2(AVLNode<K,V> *node);
        void insert2(AVLNode<K,V> *node, const K& Key, const V& Value);
        AVLNode<K,V> *root;
};

template <class K, class V>
AVLTree<K,V>::AVLTree(){
    root = nullptr;
}

template <class K, class V>
AVLTree<K,V>::~AVLTree(){
    delete root;
}
template <class K, class V>
void AVLTree<K,V>::insert(const K& Key, const V& Value){
    std::cout << "Trying to insert " << Key << ", " << Value << std::endl;
    insert2(root, Key, Value);
}

template <class K, class V>
void AVLTree<K,V>::insert2(AVLNode<K,V> *n, const K& Key, const V& Value){
    std::cout << n << std::endl;
    if(n== nullptr){
        n = new AVLNode<K,V>;
        n->Key = Key;
        n->Value = Value;
        n->parent = nullptr;
        n->left = nullptr;
        n->right = nullptr;
    }
    else if(n->Key > Key){
        insert2(n->left, Key, Value);
    }
    else{
        insert2(n->right, Key, Value);
    }
    std::cout << n << std::endl;
}

template <class K, class V>
void AVLTree<K,V>::print_AVL(){
    print_AVL2(root);
}


template <class K, class V>
void AVLTree<K,V>::print_AVL2(AVLNode<K,V> *n){
    std::cout << n << std::endl;
    if(n == nullptr){
        return;
    }
    print_AVL2(n->left);
    std::cout << "Name, ID: " << n->Value << ", " << n->Key << std::endl;
    print_AVL2(n->right);
}


#endif

My Main function looks like this:

#include "AVLTree.hpp"
#include <iostream>

int main() 
{
    AVLTree<std::string,std::string> Tree;
    Tree.insert("Hello","World");
    Tree.print_AVL();
    return 0;
}

Answer 1

Remember, even in C++ unless explicitly told otherwise parameters are pass by value Thus this:

void AVLTree<K,V>::insert2(AVLNode<K,V> *n, const K& Key, const V& Value)

coupled with this:

n = new AVLNode<K,V>;

will do little more than assign the result of the new invoke to an automatic variable n that will disappear the moment this function returns.

If you want to retain that result, pass the pointer by reference:

void AVLTree<K,V>::insert2(AVLNode<K,V>*& n, const K& Key, const V& Value)
// reference to the caller's pointer ===^

changed in both the decl and the implementation. The remaining parent pointer non-declared member I leave for you to fix, as well as the ensuing memory leak from non-destroyed children of the root-node once you start adding more nodes to the tree.