Thread: A question about the difference between Call-By-Reference and Call-by-Value

Hi all, I am still having troubles with distinguishing call by reference and call by value. Let me ask my question on an example.

Code:

struct Node{
int data;
Node *next;
Node *previous;
};
struct CircularDoublyLinkedList{
Node *final;
void create();
void empty();
void add(Node *newptr);
};
void CircularDoublyLinkedList::create(){
final=NULL;
}
int main(){
Node newnode={9,NULL,NULL};
CircularDoublyLinkedList cdll;
cdll.create();
cdll.add(&newnode);
for(int i=8;i>=0;i--){
newnode.data=i;
cdll.add(&newnode);
}
cdll.empty();
}

Here is my add method:

Code:

void CircularDoublyLinkedList::add(Node *newNode)
{
    if(final==NULL)
    {
        newNode->next=newNode;
        newNode->previous=newNode;
        final = newNode;
        return;
    }


    newNode->next=final->next;
    final->next->previous = newNode;
    final->next=newNode;
    newNode->previous=final;


}

Now, after all these things, I realized that we were sending the address of a Node-type variable. And we didn't allocate the memory dynamically for it. My questions are:

1- As far as I understood, there is only 1 node, and we're changing its data continuously in main. We are not creating another node to add to the cdll, are we?
2- Since we didn't allocate the memory dynamically, how the heck can we deallocate it ?

Your helps are greatly appreciated here Thanks.

Originally Posted by blackolick_

1- As far as I understood, there is only 1 node, and we're changing its data continuously in main. We are not creating another node to add to the cdll, are we?
2- Since we didn't allocate the memory dynamically, how the heck can we deallocate it ?

Your helps are greatly appreciated here Thanks.

1. That is correct. (And of course that's not what you want -- you want a bunch of nodes, so you need to be creating some dynamically.)
2. You don't, in the same way you don't deallocate i in your example either. It is destroyed when it goes out of scope.

Here is create:

Code:

void CircularDoublyLinkedList::create(){
final=NULL;
}

And I meant CircularDoublyLinkedList::add method.

Originally Posted by tabstop

1. That is correct. (And of course that's not what you want -- you want a bunch of nodes, so you need to be creating some dynamically.)
2. You don't, in the same way you don't deallocate i in your example either. It is destroyed when it goes out of scope.

First of all thanks for your reply, but that was my midterm question. Structures and main was given, and I was asked to write add and empty methods...

If main was given, then your add function is obligated to create a new node to add to the linked list (via new).

Originally Posted by tabstop

If main was given, then your add function is obligated to create a new node to add to the linked list (via new).

You are the man Thanks a lot.