“Invalid application of 'sizeof' to interface 'Fraction' in non-fragile ABI” in Objective-C

Question

I\'m studying Steven Kochan\'s \"Programming in Objective-C 2.0\". We created a Fraction object with two int instance variables. Later in the book Kochan uses the sizeof sta

Answer 1

The object's size could still change because you're using the modern ABI. In older versions of Objective-C, objects were basically structs and that meant it was possible to sizeof() them. This is no longer the case, and it was never a particularly good idea in the first place. I'm not sure what Kochan was trying to teach with it, but FYI this is not necessary to program Objective-C. You should be able to get the old behavior by building as 32-bit on the Mac, but again, that isn't something you'll want to do in real programs.

Answer 2

To follow up on what Chuck said, you should use class_getInstanceSize() at runtime if you really need to know the size of an object.