differentiate between recursion base case and an exception

Question

So I'm writing this height function of an avl tree class :

int avlTree::height(avlNode* tree) {
if (!tree) {
    throw invalidInput;
}
if (!tree->left && !tree->right) {
    return 0;
}
return max(height(tree->right), height(tree->left)) + 1;
}

But It feels like something is wrong, I thought of implementing it in such a way that in the beginning the tree will be checked for NULL and if it is, a 0 should be returned. But then I lose the possibiilty to check if the tree was a void pointer in the first place. Or is it fine that it'll return 0 even if it's a void pointer? what's more accepted?

thanks!

Answer 1

This is the code presented as I'm writing this answer:

int avlTree::height(avlNode* tree) {
if (!tree) {
    throw invalidInput;
}
if (!tree->left && !tree->right) {
    return 0;
}
return max(height(tree->right), height(tree->left)) + 1;
}

This will attempt to dereference a nullpointer when called with a pointer to a node whose left or right, but not both, are nullpointers.

So, the logic is ungood in the first place.

You might think about "or" versus "and", and such.

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To check for valid arguments,

• write a non-checking version, and
• write a checking version that calls the first one.

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Tip: you can use the free AStyle program to fix the indentation. Many editors also provide automatic formatting.