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return "this" is not working as expected

alansdottir (2)
Still pretty new to C++, I figured that the best place to start would be to program up some basic data structures. However, I'm encountering a problem in my Binary Search Tree's delete method. Below, I'm posting the skeleton deleteNum method (I stripped it, so it does almost nothing now), and my findNodeFromKey() methods.

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        void deleteNum(int key)
	{
		//If key is NOT in the BST, do nothing
		//If key is in the BST, find its node p

		//If p has no children, simply delete p
		//If p has one child, that child should take p's place
		//If p has two children . . .

		BinarySearchTree* p = findNodeFromKey(key);
		std::cout << p << std::endl;
		std::cout << p->data << std::endl;
		std::cout << std::endl;

	}

	BinarySearchTree* findNodeFromKey(int key)
	{
		if(data == key)
		{
			std::cout << "found " << key << std::endl;
			std::cout << this << std::endl;
			std::cout << this->data << std::endl;

			return this;
		}
		else if(data < key)
		{
			if(!rightChild){ return NULL; }
			else {
				std::cout << "search right child of " << data << " for " << key << std::endl;
				rightChild->findNodeFromKey(key);
			}
		}
		else
		{
			if(!leftChild) { return NULL; }
			else {
				std::cout << "search left child of " << data << " for " << key << std::endl;
				leftChild->findNodeFromKey(key);
			}
		}
	}


When I call BST->deleteNum(3) from my main method, here is the output I get (with added comments):

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search left child of 35 for 3
search right child of 1 for 3
found 3
0x9d0c048  		// value of the "this" pointer to be returned from findNodeFromKey()
3          		// value of this->data.  3, as expected
0xb7fbc989 		// value of the pointer p.
1082853003 		// value of p->data.  Was expecting this to be 3.


I know this is probably a very simple question, but when I made the assignment BinarySearchTree* p = findNodeFromKey(key); in deleteNum(), shouldn't p be pointing to the object returned? So shouldn't p->value = 3? What am I missing here?

Thanks in advance for looking =)
guestgulkan (2942)
I think you should be passing the return value back up the chain
So:
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.................
else if(data < key)
{
    if(!rightChild){ return NULL; }
    else {
	std::cout << "search right child of " << data << " for " << key << std::endl;
	return rightChild->findNodeFromKey(key);         //notice the return value
    }
}
else
{
    if(!leftChild) { return NULL; }
    else {
	std::cout << "search left child of " << data << " for " << key << std::endl;
	return leftChild->findNodeFromKey(key);        //notice the return value
    }
......................
alansdottir (2)
And there it is. *smacks head* Here's the new output, with guestgalkin's advised changes in place

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search left child of 35 for 3
search right child of 1 for 3
found 3
0x88b3048
3                          
0x88b3048
3                        // p->value = 3 !


I guess that I was expecting it to return correctly because the return statement was included in the if(data == key) clause. Sometimes you just need another set of eyes.

Thanks, guestgalkin!
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