Re: Possible spurious warning for isdigit() under sparc-sun-solaris2.5.1 and egcs 110597?

[Ian Lance Taylor <ian at cygnus dot com>]

   Date: Sun, 9 Nov 1997 12:13:37 -0500
   From: Daniel Eisenbud <eisenbud@cs.swarthmore.edu>

   The following macro in <ctype.h> (both in /usr/include, and egcs's fixed
   version):

   #define isdigit(c)      ((__ctype + 1)[c] & _N)   

   makes egcs -Wall emit a warning that the subscript is a char every time
   isdigit is used on a char.  First of all, perhaps this is a bug, not a
   feature.  But it seems like making Wall warn on every use of ischar,
   isdigit, etc, is bad.  Maybe fixincludes should add a cast?  (Excuse me
   if this has already been discussed - I have been following the list, but
   sometimes intermittently.

ANSI C says that the argument to all these functions must be ``an int,
the value of which is representable as an unsigned char or [...] equal
[to] the value of the macro EOF.''

If your code is passing a char, and char is signed, then your code is
indeed doing something that is worth warning about, since a negative
value for signed char is not representable as unsigned char.  This
could catch you if you ever use a machine that uses character values
greater than 127.

In my opinion you should fix your code to include the casts.  Or you
shouldn't use -Wall.  I think it's reasonable to require casts to
disable warnings.

Adding a cast to unsigned char to isdigit, et. al., would be simply
incorrect, since it would cause the macros to return the wrong value
for EOF.

Ian