passing by value

Marco

Hello, I have this problem:

void append (Node n) { //here construct the my list }
void remove(Node n) { find and remove n from the list and change the pointers as well }
void myMethod (LinkedList list, Node n) {
list.remove(n);
}

static main () {
List linkedlist = new List ll;
for (int i=0; i< 10; i++) ll.append(new Node (i));
myMethod (ll, new Node (4));
//here I'd like that linkedList wasn't changed !!!! (but it's changed)
}

Can I do value passage in this case? thanks

4 Replies

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Alan19y ago
I've had a go at coding a Clone() method to add to your LinkedList class:

     public LinkedList Clone()
     {
         LinkedList ll = new LinkedList(); //creates a new 'start' node
         Node n = start;
         Node copy = null;
         while( (n = n.Next) != null)
         {
             copy = new Node(n.Value);
             ll.addNode(copy);
         }
         return ll;
     }

Incidentally, I assume you're doing this as a project because there's already a LinkedList class in the framework, though it's doubly rather than singly linked:

http://msdn2.microsoft.com/en-us/library/he2s3bh7(vs.80).aspx
Alan19y ago
If you want to preserve the original LinkedList, then there's no alternative to copying it first.

The Nodes themselves will also need to be cloned and the pointers fixed up to point to the copies.
Marco19y ago
The point is that Iid' like perform some operation on LinkedList and these operations will change the list; However when the method go out I'd like to have the original Linked list to compute other operation on this.....I just don't like make a copy by hand of my LinkedList. I 'd like to avoid it.......
Alan19y ago
There seems to be a some confusion in your code whether you're creating a List or a LinkedList object but I'm assuming that 'll' is in fact a LinkedList variable.

Just as a general point, whenever you pass a reference type object to a method 'by value', there is nothing you can do in C# to prevent the method from changing the state of the object. There are no 'const' parameters like there are in C++ and even those can be cast away.

However, I suspect your problem is that you're trying to delete a newly created Node object from the LinkedList with this method call:

myMethod (ll, new Node (4));

You should only be deleting Node objects which already exist. So, unless you have an external reference to the Node to be removed which you can pass to the method, a better idea would be to pass the value of the Node to the method, search for that, remove the corresponding Node and fix up the pointers.