Question

I’ve a simple question (I think):
I’m trying to compare a NSNumber with a int, to see if it is 0 or 1. Here is the code:

id i = [dictionary objectForKey:@"error"]; //class = NSCFNumber

NSLog(@"%@ == 0 -> %@", i, i == 0);
NSLog(@"%@ == 0 -> %@", i, [i compare:[NSNumber numberWithBool:NO]]);

I tried this to methods but I get null as result:

2010-10-17 21:57:49.065 Api[15152:a0f] 0 == 0 -> (null)
2010-10-17 21:57:49.065 Api[15152:a0f] 0 == 0 -> (null)

Can you help me?

Answer 1

1. The result of comparison is a BOOL which is not an Objective-C object. Therefore you should not print it using %@. Try %d instead (shows 0 or 1).

2. [a compare:b] returns -1 if a < b, 0 if a == b and 1 if a > b. So your 2nd result is expected.

3. You cannot compare an NSNumber directly with an integer. That i == 0 is actually a pointer comparison which checks whether i is NULL (0), which of course is FALSE if that number exists. So the 1st result is also expected.

4. If you want to check for equality, use [a isEqualToNumber:b]. Alternatively, you could extract the integer out with [a intValue] and compare with another integer directly.

So the followings should work:

NSLog(@"%@ == 0 -> %d", i, [i isEqualToNumber:[NSNumber numberWithInt:0]]);
NSLog(@"%@ == 0 -> %d", i, [i intValue] == 0);

If the “number” is in fact a boolean, it’s better to take the -boolValue instead.

NSLog(@"%@ == 0 -> %d", i, ! [i boolValue]);