Re: how to check if a property is empty?

FROM : Jens Alfke
DATE : Sat Mar 29 18:22:34 2008

On 29 Mar '08, at 10:11 AM, Davide Benini wrote:

> I half suspected something like this...


Well, for a _pointer_ type*, there is an "empty" value: NULL. (For 
object pointers the constant 'nil' is used, but they both have the 
same underlying value.)

When an Objective-C object is created, its storage is filled with 
zeroes. So instance variables that you haven't assigned a value to yet 
are guaranteed to be NULL, or nil, or zero. (In other words, Objective-
C's 'alloc' calls 'calloc', not 'malloc'.)

But watch out — this doesn't apply to local variables in functions or 
methods. Those have random/garbage values until initialized. Same goes 
for raw memory allocated via 'malloc' — use 'calloc' if you want it 
zeroed.

—Jens

* It sounds like you're coming from a PHP background ... if you 
haven't done much C programming before, the distinction between 
pointers and scalars is likely to be confusing, since it doesn't exist 
in higher-level languages. If so, definitely find a good C textbook 
and read through that first!