Re: ObjC BOOL and boolean c expressions
Re: ObjC BOOL and boolean c expressions
- Subject: Re: ObjC BOOL and boolean c expressions
- From: Scott Ribe <email@hidden>
- Date: Wed, 05 Sep 2007 21:03:35 -0600
- Thread-topic: ObjC BOOL and boolean c expressions
> I don't know about earlier versions, but the C99 spec
> guarantees that they will return 1 if true and 0 if
> not. The logic for determining whether something is
> true or false still boils down to "zero means false,
> nonzero means true," obviously, but the operators
> themselves can only return 1 or 0.
Yes, and I do believe that logic applies to C much earlier than C99. The
"gotcha" I think is that the actual bool type performs coercion such that it
only ever holds true or false (0 or 1). So:
bool foo = 42;
if( foo == true )
Takes the branch, exactly as:
bool foo 42;
if( foo )
Would. However Objective-C BOOL, as pointed out before, is just a typedef
for a char, and YES & NO are just typedefs, so there is no coercion, so:
BOOL foo = 42;
if( foo == YES )
Would not take the branch.
Of course there is no need to ever write "if( foo == YES )", so it's an easy
problem to avoid--just learn that a variable of type bool/BOOL is an
expression of type bool/BOOL and thus does not need to be compared to a
bool/BOOL value in order to yield a bool/BOOL result.
In other words, treat C like C, not like some >20 year-old obsolete version
of Pascal or BASIC ;-)
--
Scott Ribe
email@hidden
http://www.killerbytes.com/
(303) 722-0567 voice
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