iphone - Problem with class_getInstanceSize -

I have received my class from UITabBar:

  @interface MyTabBar: UITabBar @end @ In addition, in my code, I call class_getInstanceSize for my class and system. UITabBar class:  
  size_t origisize = class_getInstanceSize ([UITabBar class] implementation MyTabBar @end  < / Pre> 
]); Size_t mySize = class_getInstanceSize ([MyTabBar class]);  
 
 I use iOS SDK 4.1. When I run on the iPhone Simulator (iPhone 4), I get the same value for the basic value and mysize. But if I run on the real device with SDK 3.1.3 then I get different values, 68 for the original and 80 for mySize. How is this possible? 
 

Most likely they changed the implementation of subclasses behind the curtains, for each OS The return of class should be logged out so that it can be ascertained whether behind your scenario behaves with the same class. Chances are you are not. They can be in the process of migrating one class to another in class cluster.