Question

I’m curious on how to implement such a function. For example,

I have something like:

class Node {
public:
int dataItem;
Node *next;
};

void foo(int number, Node & n) {
// do something
}

Then in main I need to call that function, something like this does not work:

int main () {
Node *n;
int data;
foo(data, n);
return 0;
}

I’m going to need a wrapper function in order to pass the node by reference in main and this is where I’m struggling, I’m just not sure how to approach the problem. I’ve tried some ideas, I’ve read a lot online, but I’m just not grasping it. Any help understanding how to implement this wrapper function would be fantastic.

Answer 1

You don’t have a Node at all. You just have a pointer to Node that doesn’t point anywhere in particular yet (your data is also uninitialized). A reference parameter of type Node& requires you to pass a Node, not a Node*, so what you really want is:

int main() {
  Node n;
  int data = 0;
  foo(data, n); // Pass the Node directly
  return 0;
}

Alternatively, if you really needed n to be a pointer, you could do the following:

int main() {
  Node* n = new Node();
  int data = 0;
  foo(data, *n); // Dereference n to get the Node it points to
  delete n;
  return 0;
}

However, I don’t advocate the use of raw pointers in this situation – you have to remember to delete to avoid memory leaks. You could instead use std::unique_ptr<Node> n(new Node()) instead of Node* n = new Node(), but using an Node with automatic storage duration (as in the first example) is much preferred.