When should I use nil and NULL in Objective-C?

user_97651 0
Viewed 125463

This is 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 should I use nil, NULL and [NSNull null]?

nsnull objective-c null
16 Answers

Beware that if([NSNull null]) returns true.

user_9268990

To expand on a comment from @cobbal:

MacTypes.h contains:

#ifndef nil
   #define nil NULL
#endif
user_6090

As already mentioned, they are the same, but I use either the one or the other depending on the language in which the corresponding framework was written.

For everything related to Objective-C, I use nil. For example:

- (BOOL)doSomethingWithObjectsInArray:(NSArray *)anArray {
    if (anArray == nil) return NO;

    // process elements
    ...
}

However, when checking validity of data models from a C-framework (like AddressBook framework and CoreFoundation), I use NULL. For example:

- (BOOL)showABUnknownPersonVCForABRecordRef:(ABRecordRef)aRecord {
    if (aRecord == NULL) return NO;

    // set-up the ABUnknownPersonViewController and display it on screen
    ..
}

This way, I have subtle clues in my code if I'm dealing with Obj-C or C based code.

user_8411030

Basically: nil: null pointer on an object and null: is for other type pointer

user_26359020
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