Question

Here is retaincount code.

#import <Foundation/Foundation.h>

int main (int argc, const char * argv[])
{

    @autoreleasepool {

        NSNumber *number = [[NSNumber alloc]initWithInt:10];
        NSMutableArray *array = [[NSMutableArray alloc]initWithCapacity:0];

        NSLog(@"retain count : %d",[number retainCount]);

        [array addObject:number];
        NSLog(@"retain count : %d",[number retainCount]);

        [number release];
        NSLog(@"retain count : %d",[number retainCount]);

        [number release];
        NSLog(@"retain count : %d",[number retainCount]);

        [number release];
        NSLog(@"retain count : %d",[number retainCount]);
    }
    return 0;
}

My expected answer is

retain count : 1
retain count : 2
retain count : 1
retain count : 0
and then error

but actually running result is as following.

[Switching to process 6363 thread 0x0]
2011-12-01 19:39:53.843 nsnumber[6363:707] retain count : -1
2011-12-01 19:39:53.846 nsnumber[6363:707] retain count : -1
2011-12-01 19:39:53.847 nsnumber[6363:707] retain count : -1
2011-12-01 19:39:53.847 nsnumber[6363:707] retain count : -1
2011-12-01 19:39:53.848 nsnumber[6363:707] retain count : -1

I can’t understand this result.

Why is this the result will come?

Answer 1

About retainCount

This method is typically of no value in debugging memory management
issues. Because any number of framework objects may have retained an
object in order to hold references to it, while at the same time
autorelease pools may be holding any number of deferred releases on an
object, it is very unlikely that you can get useful information from
this method.

See also

http://developer.apple.com/library/ios/documentation/Cocoa/Reference/Foundation/Protocols/NSObject_Protocol/Reference/NSObject.html#//apple_ref/occ/intfm/NSObject/retainCount

When to use -retainCount?