Problems with Doubly-Linked List iterator implementation - c++

Question

I am having some problems with a simple Doubly-Linked list class.
Here is all my code for it:
/*
* DLList.h
*
* Created on: Nov 19, 2013
* Author: tyler
*/
#ifndef DLLIST_H_
#define DLLIST_H_
#include <iostream>
using namespace std;
template <typename T>
class DLList{
private:
struct DLLNode{
private:
T data_;
bool visited_;
DLLNode* next_;
DLLNode* prev_;
public:
DLLNode(T data){
this->data_ = data;
visited_ = false;
next_ = NULL;
prev_ = NULL;
}
void setData(T data){
this->data_ = data;
}
void visit(){
visited_ = true;
}
void unvisit(){
visited_ = false;
}
void setNext(DLLNode* next){
this->next_ = next;
}
void setPrev(DLLNode* prev){
this->prev_ = prev;
}
T& getData(){
return data_;
}
bool getVisited(){
return visited_;
}
DLLNode* getNext(){
return next_;
}
DLLNode* getPrev(){
return prev_;
}
};
DLLNode* head_;
DLLNode* tail_;
public:
DLList(){
head_ = NULL;
tail_ = NULL;
}
class DLLiterator{
private:
DLLNode* node;
public:
DLLiterator(){
node = head_;
}
T& operator*(const DLLiterator& iter){
return iter.node->getData();
}
DLLiterator& operator++(const DLLiterator& iter){
if(node->getNext() != NULL)
node = node->getNext;
else
node = NULL;
return *this;
}
};
bool isEmpty(){
return (head_ == NULL);
}
void addNodeEnd(T data){
DLLNode* temp = new DLLNode(data);
if(isEmpty()){
head_ = temp;
tail_ = temp;
}
else{
DLLNode* curr;
curr = tail_;
curr->setNext(temp);
temp->setPrev(curr);
tail_ = temp;
}
}
bool contains(T data){
for(DLLNode* start = head_; start != NULL; start = start->getNext()){
if(start->getData() == data)
return true;
}
return false;
}
void remove(T data){
for(DLLNode* curr = head_; curr != NULL; curr = curr->getNext()){
DLLNode* key = curr;
if(curr->getData() == data){
if(curr == head_){
head_ = key->getNext();
key->getNext()->setPrev(NULL);
delete key;
}
if(curr == tail_){
tail_ = key->getPrev();
key->getPrev()->setNext(NULL);
delete key;
}
else{
DLLNode* prev;
DLLNode* next;
prev = key->getPrev();
next = key->getNext();
prev->setNext(next);
next->setPrev(prev);
delete key;
}
}
}
}
void printList(){
for(DLLNode* curr = head_; curr != NULL; curr = curr->getNext()){
cout << curr->getData() << "\n";
}
}
};
#endif /* DLLIST_H_ */
My problem is that I don't know how to actually use the iterator in an outside class. Everything else is tested and seems to be working fine. Still need to add a simple destructor, but my focus right now is the iterator. Any help would be great.
I tried just doing:
DLLiterator iter;
but that is clearly wrong...
EDIT: This is the operator++ code now:
iterator operator++(){
if(node_->getNext() != NULL)
node_ = node_->getNext;
else
node_ = NULL;
return *this;
}
but now it's asking for an int as an argument...?

Answer 1

Outside the class, you'd have to use the qualified name DLList<whatever>::DLLiterator. You can see that there's little point adding the wart to the nested name, unless you like your names to be hard to read: it just partly duplicates the scope name. I'd rename it iterator.
Now your problem is that it tries to initialise itself using a member of the list, head_, but it doesn't have access to a list to extract the head from. You probably want to follow the example of the standard containers, and create an iterator via a member of the list:
iterator begin() {return iterator(head_);}
and modify the iterator's constructor accordingly.
In C++11, this means users won't usually have to write out the nasty qualified name at all; you could get an iterator with
auto it = list.begin();
Finally, remove the arguments from the iterator's operator* and operator++. Since they are member functions, their operand is passed implicitly as this, not explicitly as an argument.