When to use nil and NULL in Objective C ?

Question

This is a sample code:

NSDictionary *myDictionary = [NSDictionary dictionary];
NSNumber *myNumber = [myDictionary valueForKey: @"MyNumber"];
NSLog(@"myNumber = %@", myNumber); // output myNumber = (null)


if (myNumber == nil)
    NSLog(@"test 1 myNumber == nil"); 

if (myNumber == NULL)
    NSLog(@"test 2 myNumber == NULL"); 

if ([myNumber isEqual:[NSNull null]])
    NSLog(@"test 3 myNumber == [NSNull null]");

When to use nil, NULL and [NSNULL null] ?

Thanks

Answer 1

You can use nil about anywhere you can use null. The main difference is that you can send messages to nil, so you can use it in some places where null cant work.

In general, just use nil.

Answer 2

They differ in their types. They're all zero, but "NULL" is a void *, "nil" is an id, and "Nil" is a Class pointer.

Answer 3

NULL and nil are equal to each other, but nil is an object value while NULL is a generic pointer value ((void*)0, to be specific). [NSNull null] is an object that's meant to stand in for nil in situations where nil isn't allowed. For example, you can't have a nil value in an NSArray. So if you need to represent a "nil", you can use [NSNull null.