Member Avatar for w1mark

Hi. I've been working with linked lists for a bit, but I've been having some trouble with them. My programming book does a good job in helping you make a linked list, but it does a bad job of showing you how to use them.

What I am trying to do is make an unordered linked list of classes, where you can access the function of each individual class but I'm just completely befuddled at this point. I can make the linked list store classes, but I have no clue how I would be able to "get" the classes inside the list and use their functions.

If someone could show me an example of how to use a linked of classes correctly It would be much appreciated.

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Member Avatar for Akill10

What do you mean by an unordered linked list of classes? I don't understand that bit. I think you mean objects? To "get" objects from a linked list, I suppose you mean, how to access the data at a particular node?

What you usually do, is create a separate iterator class, which will have functions like start() forward() or similar. start will create a new iterator which points to the start of your list, forward will move that pointer forward by 1 etc.. Then, to access the data at each of those nodes, you dereference the pointer.

Member Avatar for Sodabread

The only way to add classes to a linked list is to create objects/instances of those classes and add them to a list.

If you want multiple classes in the same list, you'll need to use inheritance and create child classes of a parent so they can be considered a type the same as the parent. In that case, you'll also need to know what type each one is in order to properly cast the object to get to any non-inherited functionality.

Member Avatar for w1mark

Sorry I was a little busy recently so I wasn't able to reply.

>>What do you mean by an unordered linked list of classes?
When I mean an unordered linked list of classes. I mean a linked list that stores a "singular" type of class which does not need to be sorted while/after it is inserted. My project that I am trying to do is make a building, which has a linked list floors, obviously I do not change floor #62 to floor #1 unless there is a catastrophic earthquake.(Which is unfortunately not part of my project. :()

The problem is, I just can't figure out how once I add classes to the list, how to retrieve them. I want to be able to get the first node of the list, then go through the list until I get to the desired class that I want to achieve, but so far, all I seem to be able to do is access temporary memory that resets after the next run, defeating the entire purpose of my program.

Right now though, I just decided to ditch my regular linked list and go to a doubly liked list.(a linked list with a pointer to the next and previous node). There's not much difference, It can just be run without the help of another header file. It's not my source code, but it's only for practicing purposes. I could make my own linked list, but I would basically be copying from the book anyways, except with a bunch of errors along the way and I don't have enough time for that right now.

Could someone tell me how to use this linked list though? I put a text file down below. I promise it's not for homework, I know how annoying is for someone giving you a txt file and say "do this" can be. I'm just trying to know how to use linked lists right.

Ironically, I know how to use linked stacks and queues but a regular linked list has me stumped...

#ifndef H_doublyLinkedList
#define H_doublyLinkedList

//***********************************************************
// Author: D.S. Malik
//
// This class specifies the members to implement the basic
// properties of an ordered doubly linked list. 
//***********************************************************

#include <iostream>
#include <cassert>

using namespace std;

  //Definition of the node
template <class Type>
struct nodeType
{  
    Type info;
    nodeType<Type> *next;
    nodeType<Type> *back;  
};

template <class Type>
class doublyLinkedList
{
public:
    const doublyLinkedList<Type>& operator=
                           (const doublyLinkedList<Type> &);
      //Overload the assignment operator.

    void initializeList();
      //Function to initialize the list to an empty state.
      //Postcondition: first = NULL; last = NULL; count = 0;

    bool isEmptyList() const;
      //Function to determine whether the list is empty.
      //Postcondition: Returns true if the list is empty,
      //               otherwise returns false.

    void destroy();
      //Function to delete all the nodes from the list.
      //Postcondition: first = NULL; last = NULL; count = 0;

    void print() const;
      //Function to output the info contained in each node.

    void reversePrint() const;
      //Function to output the info contained in each node
      //in reverse order.

    int length() const;
      //Function to return the number of nodes in the list.
      //Postcondition: The value of count is returned.

    Type front() const;
      //Function to return the first element of the list.
      //Precondition: The list must exist and must not be empty.
      //Postcondition: If the list is empty, the program terminates;
      //    otherwise, the first element of the list is returned.

    Type back() const;
      //Function to return the last element of the list.
      //Precondition: The list must exist and must not be empty.
      //Postcondition: If the list is empty, the program terminates;
      //    otherwise, the last element of the list is returned.

    bool search(const Type& searchItem) const;
      //Function to determine whether searchItem is in the list.
      //Postcondition: Returns true if searchItem is found in the
      //    list, otherwise returns false.

    void insert(const Type& insertItem);
      //Function to insert insertItem in the list.
      //Precondition: If the list is nonempty, it must be in order.              
      //Postcondition: insertItem is inserted at the proper place
      //    in the list, first points to the first node, last points
      //    to the last node of the new list, and count is 
      //    incremented by 1.

    void deleteNode(const Type& deleteItem);
      //Function to delete deleteItem from the list. 
      //Postcondition: If found, the node containing deleteItem is
      //    deleted from the list; first points to the first node of
      //    the new list, last points to the last node of the new 
      //    list, and count is decremented by 1; otherwise an
      //    appropriate message is printed.
      
    doublyLinkedList(); 
      //default constructor
      //Initializes the list to an empty state.
      //Postcondition: first = NULL; last = NULL; count = 0;

    doublyLinkedList(const doublyLinkedList<Type>& otherList); 
      //copy constructor
    ~doublyLinkedList(); 
      //destructor
      //Postcondition: The list object is destroyed.
      
      nodeType<Type> getFirst() const;
    //Gets the protected first pointer in list

protected:
    int count;
    nodeType<Type> *first; //pointer to the first node
    nodeType<Type> *last;  //pointer to the last node

private:
    void copyList(const doublyLinkedList<Type>& otherList); 
      //Function to make a copy of otherList.
      //Postcondition: A copy of otherList is created and assigned
      //    to this list.
};

template <class Type>
doublyLinkedList<Type>::doublyLinkedList()
{
    first= NULL;
    last = NULL;
    count = 0;
}

template <class Type>
bool doublyLinkedList<Type>::isEmptyList() const
{
    return (first == NULL);
}

template <class Type>
void doublyLinkedList<Type>::destroy()
{ 
    nodeType<Type>  *temp; //pointer to delete the node
	
    while (first != NULL)
    {
        temp = first;
        first = first->next;
        delete temp;
    }

    last = NULL;
    count = 0;
}

template <class Type>
void doublyLinkedList<Type>::initializeList()
{
    destroy();
}

template <class Type>
int doublyLinkedList<Type>::length() const
{
    return count;
}

template <class Type>
void doublyLinkedList<Type>::print() const
{
    nodeType<Type> *current; //pointer to traverse the list

    current = first;  //set current to point to the first node

    while (current != NULL)
    {
        cout << current->info << "  ";  //output info
        current = current->next;
    }//end while
}//end print


template <class Type>
void doublyLinkedList<Type>::reversePrint() const
{
    nodeType<Type> *current; //pointer to traverse 
                             //the list

    current = last;  //set current to point to the 
                     //last node

    while (current != NULL)
    {
        cout << current->info << "  ";  
        current = current->back;
    }//end while
}//end reversePrint

template <class Type>
bool doublyLinkedList<Type>::
                       search(const Type& searchItem) const
{
    bool found = false;
    nodeType<Type> *current; //pointer to traverse the list

    current = first;

    while (current != NULL && !found)
        if (current->info >= searchItem)
            found = true;
        else
            current = current->next;

    if (found)
       found = (current->info == searchItem); //test for 
                                              //equality

    return found;
}//end search

template <class Type>
Type doublyLinkedList<Type>::front() const
{
    assert(first != NULL);

    return first->info;
}

template <class Type>
Type doublyLinkedList<Type>::back() const
{
    assert(last != NULL);

    return last->info;
}

template <class Type>
void doublyLinkedList<Type>::insert(const Type& insertItem)
{
    nodeType<Type> *current;      //pointer to traverse the list
    nodeType<Type> *trailCurrent; //pointer just before current
    nodeType<Type> *newNode;      //pointer to create a node
    bool found;

    newNode = new nodeType<Type>; //create the node
    newNode->info = insertItem;  //store the new item in the node
    newNode->next = NULL;
    newNode->back = NULL;

    if(first == NULL) //if the list is empty, newNode is 
                      //the only node
    {
       first = newNode;
       last = newNode;
       count++;
    }
    else
    {
        found = false;
        current = first;

        while (current != NULL && !found) //search the list
            if (current->info >= insertItem)
                found = true;
            else
            {
                trailCurrent = current;
                current = current->next;
            }

        if (current == first) //insert newNode before first
        {
            first->back = newNode;
            newNode->next = first;
            first = newNode;
            count++;
        }
        else
        {
              //insert newNode between trailCurrent and current
            if (current != NULL)
            {
                trailCurrent->next = newNode;
                newNode->back = trailCurrent;
                newNode->next = current;
                current->back = newNode;
            }
            else
            {
                trailCurrent->next = newNode;
                newNode->back = trailCurrent;
                last = newNode;
            }

            count++;
        }//end else
    }//end else
}//end insert

template <class Type>
void doublyLinkedList<Type>::deleteNode(const Type& deleteItem)
{
    nodeType<Type> *current; //pointer to traverse the list
    nodeType<Type> *trailCurrent; //pointer just before current

    bool found;

    if (first == NULL)
        cout << "Cannot delete from an empty list." << endl;
    else if (first->info == deleteItem) //node to be deleted is  
                                       //the first node
    {
        current = first;
        first = first->next;

        if (first != NULL)
            first->back = NULL;
        else
            last = NULL;
			
        count--;

        delete current;
    }
    else 
    {
        found = false;
        current = first;

        while (current != NULL && !found)  //search the list
            if (current->info >= deleteItem)
                found = true;
            else
                current = current->next;

        if (current == NULL)
            cout << "The item to be deleted is not in " 
                 << "the list." << endl;
        else if (current->info == deleteItem) //check for 
                                                 //equality
        {
            trailCurrent = current->back; 
            trailCurrent->next = current->next;

            if (current->next != NULL)
                current->next->back = trailCurrent;

            if (current == last)
                last = trailCurrent;

            count--;
            delete current;
        }
        else
            cout << "The item to be deleted is not in list." 
                 << endl;
    }//end else
}//end deleteNode

template <class Type>
void doublyLinkedList<Type>::copyList(const doublyLinkedList<Type>& otherList)
{
	cout << "The definition of this function is left as an exercise." << endl;
	cout << "See Programming Execrise 9." << endl;
}

template <class Type>
doublyLinkedList<Type>::doublyLinkedList(const doublyLinkedList<Type>& otherList)
{
	  cout << "The definition of the copy constructor is left as an exercise." << end
Edited by w1mark because: n/a
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