Weird pointer in c++

Question

What would cause a pointer to look like this in c++? I'm building a Huffman Tree for a project and my program is segfaulting when this is one of the child nodes of the current node. This doesn't get detected by childNode == NULL either.

(TreeNode *) 0x3130303030313131

Edit, the below functions are being called in the following order: buildTree() -> generateCodes()

void HuffTree::buildTree(MinHeap * heap) {
    while (heap->getSize() > 1) {
        TreeNode * n1 = heap->removeMin();
        TreeNode * n2 = heap->removeMin();

        TreeNode * p = new TreeNode(0, (n1 != NULL ? n1->getFrequency() : 0) + (n2 != NULL ? n2->getFrequency() : 0));
    p->join(n1, n2);

        heap->insert(p);
    }

    root = heap->removeMin();
}

void HuffTree::generateCodesRecursive(TreeNode * node, int right, string code) {
    if (node == NULL) return;

    if (node->isLeafNode()) {
        codes[node->getVal()] = code;
        cout << (unsigned int) node->getVal() << " " << (int) node->getFrequency() << " " << code << endl;
    }

    generateCodesRecursive(node->getLeft(), 0, code + "1");
    generateCodesRecursive(node->getRight(), 0, code + "0");
}

void HuffTree::generateCodes() {
    generateCodesRecursive(root, 0, "");
}

Edit, heap functions:

void MinHeap::insert(TreeNode * val) {
    nodes.push_back(val);   

    int index = nodes.size() -1 ;
    while (nodes[parent(index)]->getFrequency() > nodes[index]->getFrequency()){
        swapNodes(index, parent(index));    
        index = parent(index);
    }
}

TreeNode * MinHeap::removeMin() {
    if (nodes.size() == 0) return NULL;

    TreeNode* minNode = nodes[0];

    if (nodes.size() > 0){
        TreeNode* lastNode = nodes[nodes.size()-1];
        nodes.pop_back();
        nodes[0] = lastNode;
    }

    int index = 0;
    while((left(index) < nodes.size() && nodes[left(index)]->getFrequency() < nodes[index]->getFrequency()) ||
    (right(index) < nodes.size() && nodes[right(index)]->getFrequency() < nodes[index]->getFrequency())) {
        int swapIndex = right(index) >= nodes.size() ? left(index) : (nodes[left(index)]->getFrequency() <= nodes[right(index)]->getFrequency() ? left(index) : right(index));

        swapNodes(swapIndex, index);
        index = swapIndex;
    }

    return minNode;
}

Answer 1

Couple of things to keep in mind. When you do TreeNode* p; p won't be null and will point to garbage memory, which won't be detected by if (p == NULL) or if (p == nullptr) conditions unless you explicitly set it to null during initialization.

Also, are you initializing the internal data member of TreeNode in it's constructor properly?

Answer 2

You would get such an invalid pointer value if you have some data that is not a pointer and you try to pretend it's a pointer.

The most likely way you would obtain such a pointer is from an uninitialized pointer variable. In C and C++, uninitialized variables - including pointers - may contain unpredictable "random garbage" values.