NSMutableArray's count method causes a bad access error?

Question

I see a few similar questions, but no simple answers. I'm just playing around with NSMutableArray's to get a feel for them before I actually use them in my real project. For some reason, it's giving me an EXC_BAD_ACCESS error when I try to call count on the array, and I can't figure out why.

    - (void) applicationDidFinishLaunching:(UIApplication*)application 
{   
    // Create window and make key
    _window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
    [_window makeKeyAndVisible];

    NSMutableArray* test = [[NSMutableArray alloc] initWithObjects:[NSString stringWithFormat:@"first!"], [NSString stringWithFormat:@"second!"], nil];
    [test insertObject:[NSString stringWithFormat:@"inserted"] atIndex:0];
    NSLog(@"%@", [test objectAtIndex:0]);
    NSLog(@"%@", [test objectAtIndex:1]);
    NSLog(@"%@", [test objectAtIndex:2]);
    NSLog(@"%@", [test count]); //bad access here
}

All the inserting and accessing EXCEPT the count method work just fine. I don't see why this isn't working, and would greatly appreciate some help. Thanks!

Answer 1

The %@ format specifier prints objects. The return value of -count is just an unsigned integer. You should use the format specifier %u for that type.

Answer 2

The problem is that [test count] returns an NSUInteger not a pointer (to an NSObject ). Try this instead:

NSLog(@"%u", [test count]);

Note that using %d also works, but %u is preferred.

Answer 3

- (NSUInteger)count; returns an NSUInteger .

Use this instead:

NSLog(@"%u", [test count]); //bad access here

Answer 4

count is working just fine. It does however return a NSUInteger primitive and not a pointer to a NSObject subclass. The %@ string formatter expects a point to an object and logs the NSString returned from that object's -description method. When you pass it a NSUInteger NSLog assumes it to be an object pointer and dutifully tries to send a -description message to memory address 3 which causes that EXEC_BAD_ACCESS.