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In the dealloc method for a class how would I print out the ID (or some other unique identifier) for the instance being deallocated? 

- (void)dealloc {
    NSLog(@"_deallocing: ??");
    [super dealloc];
}

Is this possible? I am just trying to get a little more feedback in the console as an aid to learning.

many thanks -gary-

fuzzygoat
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2 Answers2

54

If you specifically want the memory address of the object (which I suppose could be considered an "identifier" if you don't have one implemented in your class), you can use this:

NSLog(@"deallocing %p", self);

This can be rather helpful if you have more than one instance of a particular class and are trying to determine which is getting dealloc'd when.

dmkash
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  • Documentation about the string format specifiers: https://developer.apple.com/library/mac/documentation/Cocoa/Conceptual/Strings/Articles/formatSpecifiers.html – Maic López Sáenz Aug 06 '14 at 03:06
7

Try this:

- (void)dealloc {
    NSLog(@"_deallocing: %@", self);
    [super dealloc];
}

This will output a bit more info about the object to the console. Depending on the class, you'll either get a memory address and the class name or something more detailed. If you want to give something more detailed in your own classes, override this method and return whatever you'd like:

-(NSString *)description {
    return @"Something useful about this object";
}
iKenndac
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  • Excellent, so can I assume that "self" is simply accessing the default description of the class? – fuzzygoat Sep 09 '09 at 12:16
  • That's right - the NSLog() function replaces %@ with the given object's description. NSObject's -description method provides the default value. See here for more info on useful stuff to do with NSLog: http://www.cocoadev.com/index.pl?NSLog – iKenndac Sep 09 '09 at 12:28
  • What if you want the ID for a different class? E.g. I have a member variable `NSMutableArray` and I'd like to print its instance ID. – Rob S. Apr 20 '10 at 00:38
  • Nothing wrong with doing this--it's usually what you want--but I think dmkash's answer is better suited to the question at hand. In the case that description **is** overridden, this will not necessarily output a "unique identifier" as the question asks. – DougW Oct 21 '11 at 23:24