What values should I use for iOS boolean states?

Question

It appears that in iOS I have a number of options that seem to fit for boolean values:

YES
NO
TRUE
FALSE
true
false

Which ones should I use? In this particular case I'm hiding a label, so should I set the hidden property to YES, TRUE, or true?

Answer 1

Short answer: you should prefer YES and NO for setting foundation properties of type BOOL.

For the long answer, let's first see where are these constants defined:

• true and false are from stdbool.h; they are #define-d as 1 and 0
• TRUE and FALSE are from CFBase.h; they are #define-d as 1 and 0
• YES and NO are from NSObjCRuntime.h. This is where signed char is typedef-ed as BOOL, and its two values are #define-d as ((BOOL)1) and ((BOOL)0) or __objc_yes/__objc_no if objc_bool is supported.

The foundation classes consistently use BOOL, which is a typedef for signed char, to represent its boolean properties. Since the first two pairs get converted to int constants, using them may result in warnings, though it would probably work correctly anyway. The YES and NO constants, however, are defined in the most compatible way for your compiler, regardless of its version. Therefore, I would recommend using YES and NO consistently throughout your code.

Answer 2

Actually there is no difference between YES, TRUE and true those all represent a true state represented by 1.

And NO, false, FALSE is represents a false state represented by 0.

You can also use:

BOOL aBool = 1;

which is equivalent to BOOL aBool = true; and BOOL aBool = TRUE; and BOOL aBool = YES;

But:

BOOL bBool = 7;
if (bBool)
{
    NSLog(@"bBool is YES!\n");
}
if (bBool != YES) {
    NSLog("bBool is not YES!\n");
}

Will output like:

b is YES!
b is not YES!

This is because direct comparison with YES will fail when the value of a BOOL type is a non-zero value other than 1.

Here is a nice article for you.