Checking for a nil value

Question

Possible Duplicate:
! vs == nil in objective-c

In Objective C, is there any difference between the following two conditionals?

NSObject *obj; if(!obj) { ... }

And:

NSObject *obj; if(obj == nil) { ... }

Thanks! Just curious, figure it's a good thing to know.

...and the [complementary question](http://stackoverflow.com/questions/6366470/objective-c-if-object-vs-if-object-nil) — albertamg, Aug 10 '11 at 15:07

score 2 · Accepted Answer · answered Aug 10 '11 at 14:53

2

There is no difference between the two forms.

answered Aug 10 '11 at 14:53

Marcelo Cantos

score -1 · Answer 2 · answered Aug 10 '11 at 14:52

-1

!obj also is valid when obj=NULL or obj=@"" or empty Array etc. You get the point.

i.e. !obj is more comprehensive since you seem to be using NSObject & not any specific object type.

answered Aug 10 '11 at 14:52

Srikar Appalaraju

3

`!obj` is *not* true ("valid"?) when `obj` is `@""` or an empty array. Also, `nil` is the conventional way to denote an empty object reference, not `NULL`. – Marcelo Cantos Aug 10 '11 at 14:58
3

`!obj` is **not** true when `obj=@""` nor when it's an empty `NSArray` object. `@""` is a pointer to an `NSString` object with a length of `0`. That pointer is never `NULL` (or `nil`) since it's allocated at compile-time. – Aug 10 '11 at 14:59
want to delete this! I guess thats not possible... – Srikar Appalaraju Aug 11 '11 at 02:44

2 Answers2