Question

This portion of my current assignment has me completely stumped:

I am trying to build a LinkedList class that includes a copy constructor, which itself calls a static method (*makeCopy()). I cannot figure out how to make the makeCopy method work (all method headers were given to us in the assignment).

class ListNode
{
public:
    ListNode(double v, ListNode *p)
{
   value = v; 
   next = p;
}
private:    
   double value;
   ListNode *next;
   friend class LinkedList;    // LinkedList  has friend status 
};

// The linked list class itself
class LinkedList
{
public:
//Add number to Linked List
void add(double x)
{
    if (head == NULL)
    {
        head = new ListNode(x, NULL);
        return;
    }
    else
    {
        ListNode *nodePtr = head;
        head = new ListNode(x, nodePtr);
    }

}
LinkedList() { head = NULL; }

//Default destructor
~LinkedList()
{
    ListNode *nodePtr = head;
    while (nodePtr != NULL)
    {
        ListNode *garbage = nodePtr;
        nodePtr = nodePtr->next;
        delete garbage;
    }
}

//Copy Constructor
LinkedList(LinkedList &);

//Copy function
static ListNode *makeCopy(ListNode *pList);

private:
   ListNode * head;    

};

Below is how I am trying to write the makeCopy function:

LinkedList::LinkedList(LinkedList &list)
{
    *makeCopy(list.head);
}

static ListNode *makeCopy(ListNode *pList)
{
   if(pList->value == NULL)
   {        
       return NULL;
   }
   else
   {
    ListNode *node = pList;

    while(node != NULL)
    {
        ListNode newOne = *node;
        node = node->next;
    }
}

return;
}

First off I continue to get the error “member ListNode::value is innaccesible.” Second I’m very new to C++ and pretty sure I’m way off. If someone could help nudge me in the right direction it would be greatly appreciated. Thx

This is my current iteration of the copy constructor and the makeCopy method. Unfortunately the ListNode constructor, along with all the method headers, are part of the assignment. We have to write the code for them. The error I’m getting now is this: both return statements say “Error: a constructor or destructor may not return a value.” I’m completely lost on this one since this is just a return statement and I don’t see either a constructor or destructor.

LinkedList::LinkedList(LinkedList &list)
{
    LinkedList *copy = new LinkedList();

    while(list.head != NULL)
    {
        ListNode node = *makeCopy(list.head);
        copy->add(node.value);
        list.head = head->next;
    }

    return *copy;
 }

 ListNode * LinkedList::makeCopy(ListNode *pList)
 {
    ListNode node = *pList;

    return *node;
 }

Answer 1

static ListNode *makeCopy(ListNode *pList)

should be

ListNode * LinkedList::makeCopy(ListNode *pList)

Your version defines a free function with internal linkeage, and not defines the member.