Re: !foo vs foo == nil
Re: !foo vs foo == nil
- Subject: Re: !foo vs foo == nil
- From: "Michael Ash" <email@hidden>
- Date: Wed, 20 Aug 2008 23:06:57 -0400
On Wed, Aug 20, 2008 at 8:34 PM, Douglas Davidson <email@hidden> wrote:
> Well, after all, zero is zero, how much difference can it make? Quite a
> bit, as it turns out, since in 64-bit one of them is four bytes of zero, and
> the other is eight bytes of zero. If you're just comparing against NULL, it
> doesn't matter, but if you're using it in something where size counts--say,
> a list of vararg arguments--then it matters a lot. It's not easy to debug,
> though, because who would think that you need to distinguish one NULL from
> another?
It is a little known fact that when passing NULL (and by extension nil
or Nil) as a parameter to a vararg function, you *must* cast it to the
appropriate pointer type to guarantee correct behavior.
Interestingly, Apple's vararg methods which use nil as a terminator
(such as dictionaryWithObjectsAndKeys:) make no mention of this in
their documentation, and have a great deal of officially sanctioned
sample code which doesn't use such a cast. (And none of my code uses
it either.) I suppose Apple must be implicitly making a stronger
guarantee about the pointer-ness of nil than the C language makes
about NULL.
Mike
_______________________________________________
Cocoa-dev mailing list (email@hidden)
Please do not post admin requests or moderator comments to the list.
Contact the moderators at cocoa-dev-admins(at)lists.apple.com
Help/Unsubscribe/Update your Subscription:
This email sent to email@hidden