Operator / Iterator Deployment

Question

I'm trying to figure out a couple of things here:

• How to write an increment operator for a node class that has a pointer to the next node?

• How to implement iterators for a class as shown below?

  #include <iostream>
  #include <vector>
  using namespace std;
  
  template <typename T>
  class Node {
  public:
      Node(int i=0):val(i) {}
      Node*& operator++(int i=0) {return next;};
  
      T val;
      Node *next;
  };
  
  //================================================
  int main() {
  
      Node<int> *head, *tmp1, *tmp2;
  
      tmp1 = new Node<int>(0); 
      head = tmp1;
  
      for (int i=1; i<10; ++i) {
  
          tmp2 = new Node<int>(i);
          tmp1->next = tmp2;
          tmp1 = tmp2;
      }
  
      while (head != NULL) {
  
          cout << head->val << " '";
          head = head->operator++(0);    //How do I make it work with ++head;?
      }
  }
  

This is not a good example for demonstrating operator overloads or iterators.

Answer 1

You do not implement operator++for the class Node; you implement it for an iterator. The iterator class must be a separate class.

, , , ( val T, T, int). , int ++ : , .

template <typename T>
struct Node {
    T val;
    Node *next;

    Node(const T& t = T()) : val(t) {}
};

template <typename T>
struct node_iter {
    Node<T>* current;
    node_iter(Node<T>* current): current(current) {}

    const node_iter& operator++() { current = current->next; return *this; }
    node_iter operator++(int) {
        node_iter result = *this; ++(*this); return result;
    }
    T& operator*() { return current->val; }
};

int main() {
    // We make an array of nodes, and link them together - no point in
    // dynamic allocation for such a simple example.
    Node<int> nodes[10];
    for (int i = 0; i < 10; ++i) {
        nodes[i] = Node<int>(i);
        nodes[i].next = (i == 9) ? nodes + i + 1 : 0;
    }

    // we supply a pointer to the first element of the array
    node_iter<int> test(nodes);
    // and then iterate:
    while (test.current) {
        cout << *test++ << " ";
    }
    // Exercise: try linking the nodes in reverse order. Therefore, we create 
    // 'test' with a pointer to the last element of the array, rather than 
    // the first. However, we will not need to change the while loop, because
    // of how the operator overload works.

    // Exercise: try writing that last while loop as a for loop. Do not use
    // any information about the number of nodes.
}

, .. . . .