Question

In objective-c is the end result of !variable the same as variable==nil Also I think I read somewhere that iVars are initialized to “nil” (i.e. o) but sadly I can’t seem to find where I spotted it now. If I am correct is this initialization to nil part of declaring an iVar or is it linked to something else like @property?

i.e. do these evaluate the same …

if(!myObject) ...

and

if(myObject == nil) ...

Cheers Gary.

Edited: hopefully for more clarity.

Answer 1

Your question subject and question body appear to be asking different things, so…

To answer the question subject: No, ! and nil are not at all the same. ! is an operator that returns the logical negation of its operand (that is, !0 returns 1 and ! with anything else returns 0), while nil is a macro for 0.

To answer the question itself: Yes, !foo and foo == nil give the same result for object variables. And yes, instance variables are initialized to 0. So are static variables and global variables.