Question

What is the numeric value in the default description of a UIViewController? I had expected it to be the instance address, or perhaps the hash, but when I tested this theory this is what I got:

NSLog(@"Self [%@]", self);
NSLog(@"Address [%p]", &self);
NSLog(@"Hash [%d]", [self hash]);

2012-09-26 10:28:00.202 QuickList7[85957:c07] Self [<SelectCategoryViewController: 0xa42fc60>]
2012-09-26 10:28:00.202 QuickList7[85957:c07] Address [0xbfffdea8]
2012-09-26 10:28:00.203 QuickList7[85957:c07] Hash [172162144]

I haven’t been able to find an explanation in the reference for UIViewController or it’s superclasses – anyone know?

Answer 1

That is indeed the instance address, as for any other description implementations that use the NSOBject‘s default implementation.

But the instance address is already in the self variable, as self is of type UIViewController* and is already a pointer. Printing the pointer value of &self as you do in your example prints the address of the pointer (pointer to a pointer), not the address of the instance, as &self is indeed of type UIViewController**.

If you use NSLog(@"%p", self) instead of NSLog(@"%p", &self) you will see the same address printed as the one used by description and displayed with NSLog(@"%@", self).