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Doubly Linked Lists (copy Constructor And Assignment Operator)

Discussion in 'C++' started by japji, Jan 24, 2008.

  1. japji

    japji New Member

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    Hey Guys,

    My first post here...i'm just starting out with C++ and am stuck on a project. any advice will be appreciated...here's the code :

    Code:
    Bag::Bag(const Bag &aBag): size(aBag.size()) 
    {
    if(aBag.head == NULL) 
    head=NULL; 
    else 
    {
    head = 
    new Node; 
    assert(head != NULL);
    head->value = aBag.head->value;
    head->prev = NULL;//////////IS THIS CORREECT???
    Node *newptr = head;
    for (Node *origPtr = aBag.head->next;origPtr != NULL; origPtr = origPtr->next) 
    {
    newPtr->next = 
    new Node; 
    assert(newPtr->next != NULL);
    newPtr = newPtr->next;
    newPtr->value = origPtr->value;
    newPtr->prev = origPtr->prev; //////// IS THIS THE RIGHT WAY???
    }
    newPtr->next = NULL;
    }
    }
    where.... 
     
    struct
    Node 
    {
    ItemType value;
    Node *next;
    Node *prev;
    };
    Node *head;
    
    and Bag is obviously the class......i'm trying to make a copy constructor here for the doubly linked list but not sure of exactly how to link the PREV POINTER to the PREVIOUS node when a new node's copied.....can u help me out pls..thanks...

    ALSO IF SOME1 COULD OUTLINE AN ASSIGNMENT OPERATOR FOR THE SAME CLASS,I'D BE GREATFUL...THANKS AND TAKE CARE!
     
    Last edited by a moderator: Jan 25, 2008
  2. shabbir

    shabbir Administrator Staff Member

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    It depends on what you need to do be doing with the copy constructor but as a general solution you should even be copying the prev and next from the source node.
     
  3. japji

    japji New Member

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    but isn't that what i'm already doing with newPtr->prev = origPtr->prev...??
    i don't knw if it should be that or "newPtr->prev= head;"

    As for the copy constructor, this is the requirement we got :

    Copy constructor
    When a brand new Bag is created as a copy of an existing Bag, enough new nodes must be allocated to hold a duplicate of the original list.


    Thanks for the help
     
  4. shabbir

    shabbir Administrator Staff Member

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    Your requirement does not say anything about you are asking and so its about you to judge.
     

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