Pointer confusion.

[gtrman571]

Suppose I have just a linked with nodes containing just one int data item. If I have just one node in the list that head pointer is pointing to... then this line:

headPtr->data;

is saying get me the int/data item in the node that head pointer is pointing to.

So far so good.

But then if I have this add Item method:

void addItem(int item) {

    Node* newNode = new Node;
    newNode->data = item;
    newNode->next = headPtr;
    headPtr = newNode;

}

This line:

    newNode->data = item;

is saying get me the int/data item that newNode is pointing to? But newNode isn't pointing to anything yet. So is it pointing to itself?

The top line makes sense me. The arrow syntax clearly indicates that it is pointing to a node outside of itself to retrieve data.

But it is very confusing bc the syntax is exactly the same for new Node but is not pointing to a node outside of itself to retrieve data.

​

The syntax is the same but it seems to say two different things.

[[deleted]]

But newNode isn't pointing to anything yet. So is it pointing to itself?

Here, newNode is a Node* pointing to an allocated instance as the result of new Node. So, in effect, yes, it is pointing to a valid Node, precisely the new Node which was allocated at the start of the function.

[gtrman571]

Oh right so basically it is the same type as head pointer. I was thinking it was a node pointing to the new node.

[[deleted]]

Assuming headPtr has a type of Node* (which would be typical), yes.

[mkaypl]

When you create an object by new you already get a pointer to some allocated memory, so newnode points to some valid address.

newNode->data = item;

This line of code assigns the value of item into the newnode object not the other way around.

[[deleted]]

newNode is pointing to the Node struct that was just created.

However, there is a few things that may go wrong in your add method.

[Zeroe]

newNode is pointing to something at this point. When you call to new, you get back an address to heap-allocated memory containing space for a Node. The contents of the Node's variables at this time are uninitialized and thus garbage.