Is the LinkedList in .NET a circular linked list?

Question

I need a circular linked list, so I am wondering if LinkedList is a circular linked list?

Answer 1

No. It is a doubly linked list, but not a circular linked list. See MSDN for details on this.

LinkedList<T> makes a good foundation for your own circular linked list, however. But it does have a definite First and Last property, and will not enumerate around these, which a proper circular linked list will.

Answer 2

A quick solution to using it in a circular fashion, whenever you want to move the "next" piece in the list:

current = current.Next ?? current.List.First;

Where current is LinkedListNode<T>.

Answer 3

If you need a circular data structure, have a look at the C5 generic collections library. They have any collection that's imaginably useful in there, including a circular queue (which might help you).

Answer 4

No, its not. See MSDN

Answer 5

While the public API of the LinkedList is not circular, internally it actually is. Consulting the reference source, you can see how it's implemented:

// This LinkedList is a doubly-Linked circular list.
internal LinkedListNode<T> head;

Of course, to hide the fact that it's circular, properties and methods that traverse the list make checks to prevent wrapping back to the head.

LinkedListNode:

public LinkedListNode<T> Next {
    get { return next == null || next == list.head? null: next;}
}

public LinkedListNode<T> Previous {
    get { return prev == null || this == list.head? null: prev;}
}

LinkedList.Enumerator:

public bool MoveNext() {
    if (version != list.version) {
        throw new InvalidOperationException(SR.GetString(SR.InvalidOperation_EnumFailedVersion));
    }

    if (node == null) {
        index = list.Count + 1;
        return false;
    }

    ++index;
    current = node.item;   
    node = node.next;  
    if (node == list.head) {
        node = null;
    }
    return true;
}