Are instance variables set to nil by default in Objective-C?

Question

I'm sorting out some memory issues with my iPhone app and I've just been thinking about some basics. If I setup an ivar and never end up using it in the lifespan of my object, when I call dealloc on it, will that cause a problem? E.g.

@interface testClass {     id myobject; } @property (nonatomic, retain) id myobject; @end  @implementation testClass @synthesize myobject; - (id)init {     ...     // Do I have to set myobject to nil here?     // So if myobject isn't used the dealloc call to nil     // will be okay? Or can you release the variable without     // having set every object to nil that you may may not use      ... }  ...  // Somewhere in the code, myobject may be set to // an instance of an object via self.myobject = [AnObject grabAnObject] // but the object may be left alone  ...  - (void)dealloc {     [myobject release];     [super dealloc]; } @end 

Answer 1

Instance variables are initialized to 0 before your initializer runs..

Answer 2

Yes, ivars are always initialized to 0/nil/NULL/NO/etc.

However, if it helps you understand what's going on, go for it. The performance impact is negligible. You don't need to do it, but it won't cause any problems if you do.