From: Martin Ambuhl <mambuhl AT earthlink DOT net>
Newsgroups: comp.os.msdos.djgpp
Subject: Re: BOOL as char/int
Date: Tue, 13 Apr 1999 23:29:31 -0400
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"Rafael García" wrote:
> 
> Look at this:
> 
> #include <stdio.h>
> 
> typedef char /*int*/ BOOL;
> #define TRUE 1
> #define FALSE 0
> 
> main() {
>    BOOL flag=(BOOL)isupper('E');
>    puts(flag?"*TRUE*":"*FALSE*");
>    return 0;
>    }
> 
> It fails with BOOL as char, but works as int
> Can someone explain this reasonably?
> It works well with Borland

1) Always #include <ctype.h> when using functions prototyped there.
2) the is* family is defined to "return nonzero(true) if and only if the value
of the argument c conforms to the description of the function." (7.3.1)
isupper('E') returns 512, which is non-zero, but when assigned to a char is
subject to the implementation-defined behavior when char is signed or reduction
by modulus for unsigned char described in 6.2.1.2.  In any case, 512 % 256 = 0.

There is hardly any reason to define FALSE or TRUE (and your definition is
flawed) or to use char as the type since all standard C functions that return
true/false type answers return ints except for those which return NULL pointers
on failure.


> I have been using this typedef for years and it seems standard, robust,
> good, pretty, simple, near-machine, fast, compact...
> It seems gods of chaos are conquering the world of computing


-- 
Martin Ambuhl (mambuhl AT earthlink DOT net)
Note: mambuhl AT tiac DOT net will soon be inactive