Re: using the interfaces in ctype.h

["Greg A. Woods; Planix, Inc." <woods%planix.ca@localhost>]

(BTW, Terry, your address, tmm%mcci.com@localhost, isn't usable from mailers  
which refuse to honour broken MX CNAMEs.  MX target hosts _must_ be  
canonical hostnames, i.e. host domain names with valid A records.   
Your domain is liable to end up in the bogusmx.rfc-ignorant.org  
blacklist.)

On 18-Apr-08, at 1:19 PM, Terry Moore wrote:
> Hmm.  Back in the bad old days before C-89, casts didn't portably  
> guarantee that the result of casting was any different than what you  
> started with.  So for example isspace((uchar) x) could be wrong if x  
> was > 0xFF.
>
> I remember that the recommended practice (when using Whitesmiths C)  
> was instead:
>
>       isspace(x & 255)

Indeed!  Some implementations were so lame they didn't include the  
mask in the implementation of the macro!

Oh oh, oops, the NetBSD implementations don't seem to include the mask  
either!  I didn't realized that!  So sad.  (Which may even mean they  
violate the standards implication that they be able to safely accept  
the value of EOF.  FreeBSD, OpenBSD, and Darwin all seem to have much  
better implementations, though they are all using proper (inline)  
functions which makes it easier in some ways to do it right.)

> I think a smart compiler should be able to do the modulo 256  
> reduction without actually masking, on most platforms.  In any  
> event, when using modern compilers, the '&' will make everything an  
> int, and shouldn't cause any warnings.  (Of course, the usual  
> #defines and so forth would normally be used instead of writing  
> '255'....)

Of course that's not going to work very well at all on machines where  
a char is > 8 bits and a char is expected to have values > 0xFF.  I  
suppose one could hope for CHAR_BIT being defined correctly and create  
the mask by shifting:  ~(UINT_MAX << CHAR_BIT)

However for all it's failings, c89 is now pervasive on all unix and  
unix-like systems that are still in any way interesting or useful for  
ongoing work or play.

Hmmmm.... maybe though I should propose a patch to ctype.h that'll  
make these macros safe even in face of inappropriate uses.

--
                                        Greg A. Woods; Planix, Inc.
                                        <woods%planix.ca@localhost>