Pointer not initializing with a struct as a parameter. Access violation writing location 0x00000010.

Question

The struct looks like this:

template <class Node_entry>
Node<Node_entry>::Node(Node_entry item, Node *add_on)
{
    entry = item;
    next = add_on;
}

And the *new_rear pointer does not get initialized, but &item is filled with user input.

   Error_code Extended_queue::append(const Queue_entry &item) {
        Node<Queue_entry> *new_rear = new Node<Queue_entry>(item);
        if(new_rear = 0)
            return overflow;
        if(rear = 0){
            front = new_rear;
            rear = new_rear;
        }
        else {
            rear->next = new_rear;
            rear = new_rear;
        }
        return success;
    }

In the locals in VS2010 this and new_rear are both (!) in the next and the entry, the item is good. What am I doing to get this "Access violation writing location 0x00000010." ?

Answer 1

I assume you meant to say if (new_rear == 0), not if (new_rear = 0)? Your compiler should have given you a warning.

EDIT: In case you are wondering why it crashes - well, you're assigning 0 to the pointers, which also makes the conditions evaluate to zero, so you end up in the else block with "rear" just freshly assigned to 0, so "rear->next" ends up writing to 0x10.

Btw, this is why I always compile with the highest warning level, and warnings treated as errors. Warnings are your friends.