Implementing a doubly linked list copy constructor in C++

Question

I'm having trouble figuring out how to implement a copy constructor for doubly linked lists. The code I have so far is incorrect, I believe, because I lose track of the header node, but I'm not sure how to rectify this. Any help would be much appreciated!

DoublyLinkedList.h

#include <cstdlib>
#include <iostream>
using namespace std;
class DoublyLinkedList; // class declaration

// list node
class DListNode {
private: 
    int obj;
    DListNode *prev, *next;
    friend class DoublyLinkedList;
public:
    DListNode(int e = 0, DListNode *p = NULL, DListNode *n = NULL)
        : obj(e), prev(p), next(n) {}

    int getElem() const { return obj; }
    DListNode * getNext() const { return next; }
    DListNode * getPrev() const { return prev; }
};

// doubly linked list
class DoublyLinkedList {
protected: 
    DListNode header, trailer;
public:
    DoublyLinkedList() : header(0), trailer(0) // constructor
        { header.next = &trailer; trailer.prev = &header; }
    DoublyLinkedList(const DoublyLinkedList& dll); // copy constructor
    ~DoublyLinkedList(); // destructor
    DoublyLinkedList& operator=(const DoublyLinkedList& dll); // assignment operator


    DListNode *getFirst() const { return header.next; } // return the pointer to the first node
    const DListNode *getAfterLast() const { return &trailer; }  // return the pointer to the trailer
    bool isEmpty() const { return header.next == &trailer; } // return if the list is empty
    int first() const; // return the first object
    int last() const; // return the last object

    void insertFirst(int newobj); // insert to the first of the list
    int removeFirst(); // remove the first node
    void insertLast(int newobj); // insert to the last of the list
    int removeLast(); // remove the last node

};

// output operator
ostream& operator<<(ostream& out, const DoublyLinkedList& dll);

DoublyLinkedList.cpp - Copy Constructor

// copy constructor
DoublyLinkedList::DoublyLinkedList(const DoublyLinkedList& dll)
{
  // Initialize the list
  header = 0;
  trailer = 0;
  header.next = &trailer; 
  trailer.prev = &header;

  // Copy from dll
    DListNode* head = new DListNode;
    head->prev = dll.header.prev;
    head->obj = dll.header.obj;
    head->next = dll.header.next;

    DListNode* tail = new DListNode;
    tail->prev = dll.trailer.prev;
    tail->obj = dll.trailer.obj;
    tail->next = dll.trailer.next;

    DListNode* curr = new DListNode;
    curr->prev = head;

    while(curr != tail) {

        DListNode* n = new DListNode;
        curr->next = n;
        n = curr->prev->next;
        curr = curr->next;
    }

    curr = tail;
}

Answer 1

Rather than writing specific code to copy the list in dll using the internal structure, why not just loop through the list in dll as you normally would (using dll.getFirst() and dll.getAfterLast()) and just call insertLast with each value.