Tree Construction with pointers

I'm trying to create a function that inserts a key struct into a tree. The function sets the root correctly, but does not set the branches when called again with another key. Here is the code:

tree.h:

class tree{

    key *tree_root;

public:
    tree();
    //Constructor

    void treedestroy(key *root);
    //Tree destructor helper

    ~tree();
    //Destructor

    void insert(key* root, key *newkey, int disc);

};

insert function from tree class:

void tree::insert(key *root, key *new开发者_如何学Ckey, int disc){
    if (root == NULL){
        root = newkey;
        return;
    }
    if (newkey->cord[disc] <= root->cord[disc])
        insert(root->left, newkey, (disc+1)%4);
    else if (newkey->cord[disc] > root->cord[disc])
        insert(root->right, newkey, (disc+1)%4);
}

I'm a little inexperienced with C++ pointers and was wondering how I could fix this code so that it will fill the tree correctly?

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I'm not entirely sure about your approach here, but to help get you on your feet, it would help to use a function signature of:

void insert(key*& root, key *newkey, int disc);

This passes the root pointer by reference, which means that changes made inside the function will "stick" to the variable you passed in.

Your function as it stands modifies a function-local variable, without those changes propagating.

This article is a balanced and quick read on passing by reference (I can't say if it's the best - it was just the first decent one I found)

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1. If on the first call newkey is null, root will stay null. Make sure method call is correct.

2. I would put an else rather than an else if. If it is a binary tree it is either equal, greater, or less than.

3. Does it get into Insert_helper or not? Why did you not include it, seems important? I would guess it is getting at least that far.

---

root = newKey;

This do not modify actual root. It just modify function argument which is a copy of pointer you specify when call intsert function.

Correct version would looks something like this:

private:
void tree::insert_helper( key **root, key *newkey, int disc ) {
  if ( (*root) == NULL ) {
     *root = key;
  } else if (newkey->cord[disc] <= root->cord[disc]) {
     insert_helper( &((*root)->left), newkey, (disc+1)%4 );
  } else {
     insert_helper( &((*root)->right), newkey, (disc+1)%4);
  }
}

public:
void tree::insert( key *newKey, int disc ) {
    insert_helper( &tree_root, newkey, disc );
}

Also you have to be sure that 'key' constructol set NULL for left and right. And tree constructor should set NULL for tree_root