DoublyLinkedList. Does nothing when trying to insert between 2 nodes

Question

Im having a problem with my DLL insert function. It has no problem appending onto the list but when i have a list of 5 objects and i want to insert in between the nodes it does nothing. I have been looking around for hours to resolve this and nothing has changed.

Here is my code: Implementation in the main.cpp

cout << "\n---------------------------Insert---------------------------\n";
        //Ask the user what position they want to enter the player in.
        cout << "Enter the position you want to enter the player: ";
        int insertChoice = validators.getNum();
        //Move the iterator back to the start.
        itr.Start();
        //If the position is NOT equal to zero, Continue.
        if (insertChoice != 0)
        {
            //Loop until the position entered is reached.
            for (int i = 0; i < insertChoice; i++)
            {
                //Move the iterator forware to this position.
                itr.Forth();
            }
        //Insert the Player to the position entered by the user.
        //list.Insert(itr,stats.input());
        }
        //If the position entered is equal to zero, Continue.
        else
        {
            //Append onto the list.(Add it onto the start).
            list.Append(stats.input());
        }

Insert function in the header file.

// ----------------------------------------------------------------------------------------------------------------
//  Name:           Insert
//  Description:    Inserts data before the iterator, this works whether the iterator is backwards of forwards
//                  through the list.Inserts at the end of the list if iterator is invalid.
//  Arguments:      p_iterator: The iterator to insert before
//                  p_data: the data to insert
//  Return Value:   None.
// ----------------------------------------------------------------------------------------------------------------
    void Insert(DoublyLinkedListIterator<Datatype>& p_itr, Datatype p_data)
    {
        if(p_itr.m_node != 0)
        {
            // insert the data before the iterator
            p_itr.m_node->InsertBefore(p_data);

            //if the iterator was at the head of the list,
            //reset the head pointer
            if(p_itr.m_node == m_head)
            {
                m_head = m_head->m_prev;
            }
            // increment the count
            m_count++;
        }
        else
        {
            Append(p_data);
        }
    }

Append

void Append(Datatype p_data)
    {
        if(m_head == 0)
        {
            // create a new head node.
            m_head= m_tail= new DoublyListNode<Datatype>;
            m_head->m_data= p_data;
            m_head->m_next= 0;
            m_head->m_prev= 0;
        }
        else
        {
            // insert a new node after the tail and reset the tail.
            m_tail->InsertAfter(p_data);
            m_tail= m_tail->m_next;
        }
        m_count++;
    }

InsertBefore

// ----------------------------------------------------------------
//  Name:           InsertBefore
//  Description:    This adds a node before the current node.
//  Arguments:      p_data - The data to store in the new node.
//  Return Value:   None.
// ----------------------------------------------------------------

void InsertBefore(Datatype p_data)
{
    //Create new Node
    DoublyLinkedListNode<Datatype>* newNode = new DoublyLinkedListNode<Datatype>;
    newNode->m_data = p_data;
    //Set up new Node Pointers
    newNode->m_next = this;
    newNode->m_prev = m_prev;
    //if theres a node before it, make it point to new node
    if(m_prev != 0)
    m_prev = newNode;
}

I dont think the problem lies int the implementation in the main but rather in the actual insert function. Thanks in advance, Becca.

Answer 1

InsertBefore

newNode->m_next = this;
newNode->m_prev = this->m_prev;

you need to tell this to point (as previous) to the new node too.

newNode->m_next = this;
newNode->m_prev = this->m_prev;
this->m_prev->m_next = newNode;
this->m_prev = newNode;

---

This should also be

Insert function in the header file.

 if(p_itr.m_node == m_head)
 {
      m_head = p_itr->m_prev;
               ^^^^^^
 }