On May 26, 2011, at 8:32 PM, Graham Cox wrote: > > On 27/05/2011, at 11:23 AM, Quincey Morris wrote: > >> On May 26, 2011, at 18:00, Graham Cox wrote: >> >>> unsigned seed = (unsigned)([NSDate timeIntervalSinceReferenceDate] * >>> 10000.0); >>> >>> NSLog(@"launched, seed = %ld", seed ); >> >> Also, be careful here, because %ld is the wrong format specifier for type >> 'unsigned'. Whether it logs the right value is going to be architecture >> dependent. > > Ok, then that raises the question what should I use?
%u > I'm confused about how to correctly write format specifiers for both 32 and > 64-bit runtimes. The 64-bit porting guide doesn't spell it out (yet you end > up with code peppered with warnings that you should examine the use of the > format specifier without docs properly explaining their correct use). It's > also not clear to me whether just 'unsigned' is a fixed-size quantity or not, > depending on architecture. Just "unsigned" is shorthand for "unsigned int". Between the Mac's 32-bit and 64-bit architectures, int doesn't change size. That can't be generalized, although it's darn-near universal. However, that's irrelevant. The format specifiers don't indicate a size. They indicate a type. For "unsigned", you use "%u". That's the end of the story. > Someone mentioned that random() has been superseded. Again??! It seems to me > that random number generators get superseded every other week. How is anyone > supposed to know what is considered current best practice? Especially as for > such functions there doesn't seem to be a simple way to see in man pages or > other documentation what's deprecated. random() has not been deprecated or even superseded. arc4random() has higher quality pseudo-randomness, which is probably what prompted the claim, but as David Duncan said that doesn't justify the claim. It's a question of tradeoffs. arc4random() is slower and non-reproducible. (The slowness may matter in this case, where I asserted it doesn't matter when seeding, because you usually seed once and generate many times.) Regards, Ken _______________________________________________ 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 arch...@mail-archive.com
