Re: using the interfaces in ctype.h

On Wed, Apr 16, 2008 at 10:24:41PM -0400, Greg A. Woods;
Planix, Inc. wrote:
> 
>  On 16-Apr-08, at 6:30 PM, Christos Zoulas wrote:
> > - cast ctype arguments to unsigned char and not
int, otherwise you silence
> > the warning but you can still get a core-dump.
> 
> 
>  If you're talking about the is*() and to*() APIs from
libc then that doesn't 
>  seem to make any sense for a standards compatible
program.
> 
>  The definitions in all of the standards, an in the
NetBSD manual pages, all 
>  request that the parameters for these functions are to
be passed as (int).
> 
>  Unfortunately even various NetBSD architectures, at
least for some releases, 
>  are inconsistent in how these interfaces are defined
and what warnings are 
>  given for various usages.  I've had the best luck
getting the least warnings 
>  on a wide variety of platforms by always casting to
(int) too.

These functions accept int only because they need to handle
(-1) argument,
i.e. possible result of getc(3). I.e. valid character code
range is
from -1 to 256.

If char is signed (it is on NetBSD/i386 IIRC), by casting to
int
you get negative number and the array access done by is*()
macros
causes coredump (or overwrites some memory).

You must cast argument of is*() to (unsigned char) always
first. You can
do (int)(unsigned char) cast if just (unsigned char) gives
you a warning.

Jaromir
-- 
Jaromir Dolecek <jdolecekNetBSD.org>           
http://www.NetBSD.cz/
-=- We can walk our road together if our goals are all the
same;     -=-
-=- We can run alone and free if we pursue a different aim. 
        -=-