Comments on: Of BOOL and YES

By: Michel Colman

Michel Colman — Thu, 28 Jan 2010 07:30:04 +0000

By the way, it is also perfectly safe to use “true” and “false” instead of the ugly upper case “YES” and “NO”. You won’t find a single YES or NO in my code, and it works just fine. Whenever setting a BOOL to true, the compiler automagically inserts a YES (implicit conversion of BOOL to bool). The resulting code is the same, maybe it will add a millisecond or so to my total compile time, and I guess a few bytes to the size of my code since YES and NO are shorter words, but otherwise it makes zero difference.

By: Michel Colman

Michel Colman — Thu, 28 Jan 2010 07:21:02 +0000

It is perfectly safe to use
bool b = myBOOL;
and
myBOOL = b;

These are exactly equivalent to your complicated question mark constructions. For example:

bool b = 3.141592654;
will set b to true. Conversion of anything to bool will set it to true if the original was not zero, and to false otherwise. No need to use “? true: false” because that’s what a conversion to bool does by definition.

In the other direction, a bool will always be converted to 0 or 1, which corresponds to NO and YES in the BOOL type, so no worries there, either.

An “if” condition is also implicitly converted to bool, so the same applies there.

The only thing you should avoid, is explicitly comparing to YES.

By: Steve

Steve — Fri, 27 Feb 2009 16:14:49 +0000

That works fine. Basically the compiler is comparing to zero, which is why you can do stuff like:

char* cp = some_address;
if (cp) {
// do something if cp != 0
}

if (!cp) {
// do something if cp == 0
}

So, the magic is in the ! operator. Given:

! value

the result is of type int and is the “logical negation” of the value:

0 if value is nonzero;
1 if value is 0.

You can also say that the expression:

! value

is equivalent to:

(0 == value)

Notice that this explicitly avoids comparing with YES (or 1), which was the main point of my original note.

HTH!

By: secretsquirrel

secretsquirrel — Fri, 27 Feb 2009 04:14:55 +0000

a question:
in objective-c and iphone development,
do both BOOL and bool allow setting with ! to toggle to the opposite?

example:
myBOOL = !myBOOL;
newBOOL = !myBOOL;

and so on.

can i pass a message to a method with !myBOOL?

By: pRAMOD

pRAMOD — Fri, 13 Feb 2009 05:04:36 +0000

Good post……most usefull !!

By: adolfo

adolfo — Sat, 17 Jan 2009 07:43:27 +0000

Great post, man. Concise and very useful. It’ll probably save me hours of frustrating debugging in the future.