Ok to release a pointer thats nil?

Question

If I create a new object that includes two object pointers (see below) when the object is created the pointers are set to point to nil;

@interface rocketShip : NSObject {
    NSString *name; 
    NSNumber *thrust;
}

If (for some unexpected reason) I don't assign these pointers and later release them in my dealloc method is that ok, I am pretty sure it is, just wanted to check?

- (void)dealloc{
    [name release];
    name = nil;
    [thrust release];
    thrust = nil;
    [super dealloc];
}

gary

Answer 1

Sending a message to nil won't cause an error, so this is fine. You need to make sure the pointers are actually nil though - sending a message to a garbage pointer will likely cause errors.

Answer 2

Yes, you can do this because you can safely send a message (such as release) to nil and it will just do nothing.

Answer 3

If you use the accessor property to create your get/set methods:

@interface rocketShip : NSObject {
    NSString *name; 
    NSNumber *thrust;
}

@property (retain, nonatomic) NSString *name;
@property (retain, nonatomic) NSNumber *thrust;

And in your .m file:

@synthesize name;
@synthesize thrust;

You can then just set your variable to nil in dealloc. This will in fact call your setter and decrement the reference count by one and clean things up.

Answer 4

It’s important in Objective-C to distinguish between objects and variables. You cannot release a pointer (the value of a variable), you can only release an object (the object to which a pointer refers). A nil pointer refers to no object, so messages sent to nil do nothing (which is generally safe).