First: I just realized that one of my statements was incorrect;
NSString *string2 = [[NSString alloc] initWithFormat:@"mySecondString"]; does not make string2 retainCount to be 2147483647, it only becomes 2147483647 when inserting @"" instead of @"mySecondString" And regarding why use retainCount? Well I am trying to find where is my mistake, since sometimes my application crashes and I am quite (99.9%) sure that I am releasing a object that shouldn't be. Any ideas how to find such a bug? Thanks in advance. Regards Ignacio. On Thu, May 28, 2009 at 12:14 AM, Sherm Pendley <sherm.pend...@gmail.com> wrote: > On Wed, May 27, 2009 at 9:59 AM, Ignacio Enriquez <nach...@gmail.com> wrote: >> >> 1.- What is the difference between string1 and string2? where >> NSString *string1 = [NSString stringWithFormat:@"myFirstString"]; >> NSString *string2 = [[NSString alloc] initWithFormat:@"mySecondString"]; > > You own string2 and must release it when you're done with it. > > You do not own string1 and must not release it. > >> >> I thought that string1's memory allocation and release would be done >> by the system (autoreleased) and string2's memory and release should >> be done by me (by [string2 release]) >> Am i mistaking? > > Yes, you are mistaken. :-( > > The memory contract concerns ownership - i.e. what are the calling code's > responsibilities with respect to retain and/or release. Many objects that > you do not own are in fact autoreleased, but there is no guarantee of that. > The only guarantee concerns whether the caller owns the returned object. > That contract works both ways; the called code is also required to return an > object that behaves correctly if the caller fulfills its end of the > contract. *How* the called method does so is an implementation detail that's > not part of the contract, and something the caller need not care about. > >> A funny thing is when doing: >> NSLog(@"retainCount %i %i", [string1 retainCoung], [string2 retainCount]); >> I got : >> "retainCount 2147483647 2147483647" >> >> So It seems that both objects are autorelease objects... Why is that? >> I thougth that string2 retainCount would be 1. > > With no placeholders in your format, NSString is perfectly within its rights > to return a singleton instance that represents the constant static string > that's compiled into your binary. For such singletons, the retain count is > often set to a "special" value that the -release method will recognize as > meaning "can't touch this." So no, these objects are not autoreleased. > > But, it doesn't matter. All that your code needs to do is follow the > contract, and release string2 when it's done with it. > >> 2.- How can I get two simple NSString instances with a retainCount equal >> to 1 > > You can't depend on any particular value of retainCount. You shouldn't even > be looking at it - as you've seen, it's an internal implementation detail > that can (and does) have values that are only meaningful if you're > maintaining the target class - in this case, NSString. > > Take a step further back - what problem are you having, that led you to > think that looking at retainCount would help you solve it? > > sherm-- > > -- > Cocoa programming in Perl: http://camelbones.sourceforge.net > > _______________________________________________ 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
