Saving binary tree data to disk

I've made an implementation of this program using a binary tree. It works fine, but I'd like to save my decision tree to the disk because I don't want to lose the result of my "teaching". Do I have to invent my own file format and write a parser for it or is there a more simple method? Where should I start? Any suggestions are welcome.

just write it out using any (deterministic) tree traversal method, then you can read it back knowing where everything goes.

A nice method is to use implied indices. The root is at index 1, then for any node at index i, store the left child at position 2*i and the right child at position 2*i + 1. Then you just have an array representing your tree.

Perspective, thanks for your advice, it helped a lot.

I'm trying to do a preorder traversal on my tree and write a bool value and the node text into the file in the order of the traversal. It doesn't work (it creates a file with a single line containing the data for the root). I'm clueless because it works when I'm writing on the console. The only difference is that I'm writing into a different stream. Or is it?

Include this in the file I posted above:

Code:

---

void PreorderOutput(NodePtr ANode)
{
    ofstream out_stream;
   
    out_stream.open("data.txt");
   
    out_stream << ANode->IsAnswer << ANode->Text << "\n";
    cout << ANode->IsAnswer << ANode->Text << "\n";
   
    if (!ANode->IsAnswer)
    {
        PreorderOutput(ANode->YesPtr);
        PreorderOutput(ANode->NoPtr);
    }
    out_stream.close();
}

---

You're creating a new stream every time you recurse into PreorderOutput(). You need to make the stream object a singe instance throughout the recursion. You can do that by making it global or by making it a parameter to PreorderOutput().

gg

Oh thanks. I'm a bit tired (it's 6am here - I think I'm getting addicted to programming :) ).

>> I think I'm getting addicted to programming
<cartman>"Sweet"

gg

The simplest method would be to iterate through the tree, save the current node, save the yes node, save the no node, then move on to the next.
Note that saving strings using << is fine, but saving a bool using << will probably produce something like 0 or 1 in the file since it stores it as text. Also note that with bools, this isn't a problem, but if you're planning to store other data that is longer than 1 byte (int, for example), then it's better to use istream.write and istream.get since they work with binary data.

I think operator << will stop reading a string when it hits space or '\0', so length shouldn't be an issue.

Elysia,
Thanks for your reply.
I searched Wikipedia for tree traversal and found my algorithm there. I think what you are (and Perspective has been) suggesting is a level order traversal, but it seems to me that although it would also work, preorder traversal is a lot simpler and does effectively the same thing (crawling through the tree in a predictable way). If I save a bool for every node that tells if that node is an end node (or 'leaf' or whatever it is called), it produces an output from which the tree can be recreated in memory using the same algorithm.

Thx for your advice on the << operator and the istream functions. It made a lot of things clear.

I believe that way is kindof like what I suggested. Traverse the yes node, save the answer and if there's another yes node, then call itself and traverse that until NULL.
After that, traverse the NO node.
...And all the way back to root.
The only problem is loading the list back into memory which might not be so easy.

Finally my little program is running without errors. Thank you for all the advice, you guys are really helpful. I'm uploading the code, so if you have time, please have a look at it. I would welcome any comments on it.