On Wed, Aug 20, 2008 at 8:31 PM, Andrew Farmer <[EMAIL PROTECTED]> wrote: > On 20 Aug 08, at 20:06, Michael Ash wrote: >> >> On Wed, Aug 20, 2008 at 8:34 PM, Douglas Davidson <[EMAIL PROTECTED]> >> 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. > > Source (and, preferably, example) please? A pointer is a pointer is a > pointer; the internal representation of (char *) NULL is identical to (void > *) NULL or (NSRect *) NULL or (id) nil or what-have-you.
The C standard doesn't require that NULL has a pointer type. The following is a perfectly valid definition of the NULL macro: #define NULL 0 If you pass that to a vararg function, it will be passed as if it were an int. >From the C standard: "An integer constant expression with the value 0, or such an expression cast to type void *, is called a null pointer constant." -- Clark S. Cox III [EMAIL PROTECTED] _______________________________________________ Cocoa-dev mailing list (Cocoa-dev@lists.apple.com) 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: http://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com This email sent to [EMAIL PROTECTED]
