Re[2]: Problem with +numberWithBool: ?

[Manuel Guesdon]

On Sat, 31 Jan 2004 00:04:45 +0100 "Pascal J.Bourguignon" <address@hidden> 
wrote:
 >| It's a C (or Objective-C) question: does a==b (or a<b, etc) return 0/1
 >| or 0/possibly anything else than 0 ?
 >| 
 >| On 680x0 processors, the instructions that build boolean values give 0
 >| and 0xff  ((char)(-1)). All C  compilers I've see on  these processors
 >| always take care to mask it off to 0/1. 
 >| 
 >| I  don't have  my ANSI-C  references at  hand, but  if it's  said that
 >| boolean producing  operators always  return 0 or  1, then there  is no
 >| problem,  returning a  boolean expression  will  return a  BOOL (or  a
 >| bool).
 >| 
 >| 
 >| In  any  case,  that's  one  more  reason why  it's  better  to  write
 >| if(condition) rather than if(condition==YES).


A  reference:
        http://www.lysator.liu.se/c/c-faq/c-8.html
<<
8.2: Isn't #defining TRUE to be 1 dangerous, since any nonzero value is 
considered "true" in C?  What if a built-in boolean or relational operator 
"returns" something other than 1?

It is true (sic) that any nonzero value is considered true in C, but this 
applies only "on input", i.e. where a boolean value is expected.  When a 
boolean value is generated by a built-in operator, it is guaranteed to be 1 or 
0.  Therefore, the test

        if((a == b) == TRUE)

will work as expected (as long as TRUE is 1), but it is obviously silly.  In 
general, explicit tests against TRUE and FALSE are undesirable, because some 
library functions (notably isupper, isalpha, etc.) return, on success, a 
nonzero value which is not necessarily 1.  (Besides, if you believe that "if((a 
== b) == TRUE)" is an improvement over "if(a == b)", why stop there?  Why not 
use "if(((a == b) == TRUE) == TRUE)"?)  A good rule of thumb is to use TRUE and 
FALSE (or the like) only for assignment to a Boolean variable or function 
parameter, or as the return value from a Boolean function, but never in a 
comparison.
>>


Manuel



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