Question

I am writing a binary tree, started getting errors, so I’ve removed all my templating, but it still won’t compile, stumped by my final error!
Writing a recursive add function, but not sure how to add my new dataClass to my tree when it finds an empty node

#pragma once
#include <cstring>

typedef dataClass T;
//template <class T>
class treeNode
{
private:
treeNode* _greaterNode;
treeNode* _lessNode;
T _data;
public:
treeNode(T data);
void add(T data);
void del(T data);
};

//template <class T>
treeNode/*<T>*/::treeNode(T data)
{
_data = data;
_greaterNode = _lessNode = NULL;

}
//template <class T>
void treeNode/*<T>*/::add(T data)
{
if(_data == NULL)
{
    // add here
    this = new treeNode(data);
}
else if(data > _data)
{
    // data is bigger go to greater
    this->_greaterNode->add(data);
}
else if(data < _data)
{   
    // data is lower go to less than
    this->_lessNode->add(data);
}
else
{
    // data the same, throw exception
}
}

It’s breaking on:

if(_data == NULL)
{
    // add here
    this = new treeNode(data);
}

Answer 1

You can not assign to this! You could assing to *this, like in *this = treenode(data);, but that could probably lead to other errors as the node pointer would be overwritten.

Why not simply set _data to the parameter data?

Also, when doing the recursive call you should create the links if they do not exist:

else if(data > _data)
{
    // data is bigger go to greater
    if (this->_greaterNode == NULL)
        this->_greaterNode = new treeNode(data);
    else
        this->_greaterNode->add(data);
}