Crashing

This is a discussion on Crashing within the C++ Programming forums, part of the General Programming Boards category; Hello, First of all, this is my code: Code: #include <iostream> using namespace std; struct TreeNode { int data; struct ...

  1. #1
    Registered User
    Join Date
    Mar 2009
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    1

    Crashing

    Hello,

    First of all, this is my code:

    Code:
    #include <iostream>
    
    using namespace std;
    
    struct TreeNode
    {
        int data;
        struct TreeNode *left;
        struct TreeNode *right;
    
        TreeNode() { left = NULL; right = NULL; }
    };
    
    void insertNode(int data, TreeNode* t)
    {
        if(data <= t->data)
        {
            // insert left
            if(t->left == NULL)
            {
                cout << "INSERTING LEFT OF " << t->data << endl << endl;
                TreeNode newt;
                newt.data = data;
                t->left = &newt;
    
            }
            else
                insertNode(data, t->left);
        }
        else
        {
            // insert right
            if(t->right == NULL)
            {
                cout << "INSERTING RIGHT OF " << t->data << endl << endl;
                TreeNode newt;
                newt.data = data;
                t->right = &newt;
            }
            else
                insertNode(data, t->right);
        }
    }
    
    int main()
    {
        TreeNode a;
        TreeNode b;
        TreeNode c;
    
        a.data = 5;
        b.data = 50;
        c.data = 20;
    
        a.right = &b;
        b.left = &c;
    
        insertNode(80, &a);
    
        cout << "The right child of the new node is: " << b.right->right << endl;
        cout << b.right->right << endl << endl;
    
        if(b.right->right == NULL)
            cout << "ITS NULL";
        else
            cout << "ITS... NOT";
    
        return 0;
    }
    I've just started out with C++ and I'm playing with binary trees. In InsertNode(), a new Node with the data 80 is added to the right of the 'b' node, meaning that b.right is that new node. Now, when displaying b.right->right (which should be NULL), I'm getting some weird stuff.

    The first cout (starting with 'the right child of...') gives me a memory address, the second cout gives me 0. When checking if b.right->right == NULL, I get the message that it's not.

    Why is this happening? When I create a new node, both the children are instantiated to NULL but apparently something goes wrong when I do this in the InsertNode() function.

  2. #2
    int x = *((int *) NULL); Cactus_Hugger's Avatar
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    You are allocating your treenodes on the stack. The pointers you keep to them are invalid the moment they are destructed (when if(t->right/left == NULL) closes).
    In code:
    Code:
    	// insert right
    	if(t->right == NULL)
    	{
    		cout << "INSERTING RIGHT OF " << t->data << endl << endl;
    		TreeNode newt;
    		newt.data = data;
    		t->right = &newt;
    	} // newt is destructed here, and t->right now points to invalid memory.
    More than likely, you must dynamically allocate them. Research 'new' and 'delete'
    long time; /* know C? */
    Unprecedented performance: Nothing ever ran this slow before.
    Any sufficiently advanced bug is indistinguishable from a feature.
    Real Programmers confuse Halloween and Christmas, because dec 25 == oct 31.
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    recursion (re - cur' - zhun) n. 1. (see recursion)

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