Objective-c – difference between YES/NO,TRUE/FALSE and true/false in objective-c


Simple question really; is there a difference between these values (and is there a difference between BOOL and bool)? A co-worker mentioned that they evaluate to different things in Objective-C, but when I looked at the typedefs in their respective .h files, YES/TRUE/true were all defined as 1 and NO/FALSE/false were all defined as 0. Is there really any difference?

Best Solution

I believe there is a difference between bool and BOOL, check out this webpage for an explanation of why:

Because BOOL is an unsigned char rather than a primitive type, variables of type BOOL can contain values other than YES and NO.

Consider this code:

BOOL b = 42;

if (b) {
    printf("b is not NO!\n");

if (b != YES) {
    printf("b is not YES!\n");

The output is:

b is not NO!
b is not YES!

For most people this is an unnecessary concern, but if you really want a boolean it is better to use a bool. I should add: the iOS SDK generally uses BOOL on its interface definitions, so that is an argument to stick with BOOL.