BST - inserting + C++ - c++

Question

I'm trying to work on a binary search tree data structure, but I cannot seem to accomplish inserting anything into the tree. Every time my program calls the insert function, it believes there is nothing in tree. Here are the 2 classes:
template<typename T>
class TreeNode{
public:
T m_data;
TreeNode* m_right;
TreeNode* m_left;
TreeNode<T>(const T& data, TreeNode<T>* right, TreeNode<T>* left) : m_data(data), m_right(right), m_left(left){};
};
template<typename T>
class MyBSTree : public AbstractBSTree<T>{
protected:
TreeNode<T>* m_root;
int m_size;
And here is the function:
void rec_insert(TreeNode<T>* root, const T& x){
if(root == NULL){
cout << "Inserting here" << endl;
TreeNode<T>* tmp = new TreeNode<T>(x, NULL, NULL);
root = tmp;
}
else if(x < root -> m_data){
cout << "Inserting left" << endl;
rec_insert(root -> m_left, x);
}
else if(x > root -> m_data){
cout << "Inserting right" << endl;
rec_insert(root -> m_right, x);
}
if(root == NULL)
cout << "WHAT IS HAPPENING?" << endl;
cout << "resizing" << endl;
m_size++;
};
The output for inserting a couple of items is this:
Inserting here
resizing
Inserting here
resizing
I really have no clue what is going on here, any help would be greatly appreciated.

Answer 1

You need to do a bit of research on pass by reference and pass by value.
You pass a pointer into your insert method - you can only change the value of root locally - any change you make won't persist beyond the function call. You need to pass by reference to allow root to be changed and see that change outside the rec_insert() method.
Another approach may be to refactor your code to return the root value from rec_insert().