Thread: Linked List Iterator

I know there must be lots of these posted, but I search on google and on here, and I'm still having trouble.

We still haven't covered iterators fully and I'm having trouble with it. If anyone has a link to how iterators work (w/anything) that includes code, please let me know.
Anyway, I have a linked list class and an iterator class. I'll just try to post the relevant code.

One of the errors that I get is a warning that a reference to local variable 'it' is returned. I think I understand the error, but I'm not sure how to solve it. Any help is appreciated. Thanks.


**********LINKEDLIST CLASS AND MAIN***********
// LinkedList and main are together. they're not separate files.

Code:

#include <iostream>
#include <conio.h>

using namespace std;


template <class T>
class Node
{
public:
    T data;
    Node<T>* next;
    Node<T>* prev;
    Node(){ next = NULL; prev = NULL;}
};

#include "ListIterator.h"

template <class T>
class LL
{
    public:
        LL();
	ListIterator<T> &begin();
	ListIterator<T> &end();
    private:
        Node<T>* head;
        friend class ListIterator<T>;
}; 

template <class T>
ListIterator<T>& LL<T>::begin()
{
    ListIterator<T> it(head);
    return it;
} 

template <class T>
ListIterator<T>& LL<T>::end()
{
    // This is wrong... I'm not sure how to do this...
    ListIterator<T> it(head);
    while(it.hasNext())
    return it;
}

int main()
{  
    LL<int> obj;
    obj.pushFront(3);
    obj.pushFront(4);
    //obj.printList(cout);
    
    ListIterator<int> iter = obj.begin();

    getch();
    return 0;
}

*********LISTITERATOR CLASS*************

Code:

using namespace std;
template <class T>
class ListIterator
{
   public:
	  Node<T> *current;
	  ListIterator() {}
	  ListIterator(Node<T>*);
	  bool hasNext();  
      bool hasPrevious();
	  T next();
	  T previous();
	  void insert(T val);
	  void remove();
};


// 
template <class T>
ListIterator<T>::ListIterator(Node<T> *head)
{
    current = head;
}

    
// Returns true if it has a next node
template <class T>
bool ListIterator<T>::hasNext()
{
	return (current->next == NULL);
}

// Returns true if it has a previous node
template <class T>
bool ListIterator<T>::hasPrevious()
{
	return (current->previous == NULL);
}

// Returns next node's data
template <class T>
T ListIterator<T>::next()
{
	if(!this->hasNext())
		return;
	return (current->next->data);
}

// Returns previous node's data
template <class T>  
T ListIterator<T>::previous()
{
	if(!this->hasPrevious())
		return;
	return (current->prevous->data);
}

template <class T>
void ListIterator<T>::insert(T val)
{
	Node<T> newNode = new Node<T>(val);
	if(this->hasNext())
	{
		newNode->back = current;
		newNode->next = current->next;
		current->next->back = newNode;
		current->next = newNode;
	}
	// Last one in list
	else if(this->hasPrevious())
	{
		newNode->back = current;
		current->next = newNode;		
	}
}

// Remove function
template <class T>  
void ListIterator<T>::remove()
{
	if(current == NULL)
		return;
	current->next->back = current->back;
	current->back->next = current->next;
	delete current;

}