------- Comment #3 from edwintorok at gmail dot com 2008-11-07 17:14 -------
(In reply to comment #2)
> Subject: Re: New: 'warning: comparison between signed and
> unsigned' shouldn't be given for equality comparisons
>
> On Fri, 7 Nov 2008, edwintorok at gmail dot com wrote:
>
> > Consider this code:
> >
> > int foo(int a, unsigned b)
> > {
> > return a != b;
> > }
>
> > $ gcc -O2 -Wall -W foo.c -c
> > foo.c: In function foo:
> > foo.c:3: warning: comparison between signed and unsigned integer expressions
>
> Seems correct to me. You could have a == -1 and b == UINT_MAX and they
> would compare equal, but it's not at all obvious from the code that this
> is the user's intent; and if it is their intent, they can use an explicit
> cast.
It would be nice to have a separate warning option for ==, != comparisons, and
another for <,>,<=,>= comparisons.
The problem is that with code that uses read(2) and write(2) you get lots of
warnings, and adding casts is time-consuming and of little benefit.
I'd like to turn -Wsign-compare into -Werror for 'make distcheck' in my
project, but can't do that due to the != comparisons. If I would have a
distinct -W flag for it, I could -Wno-error that.
>
> > FWIW, if I change int to 'short int' or 'signed char' (and unsigned
> > appropriately) I get no warning.
>
> Both short and unsigned short will be promoted to int before the
> comparison, so you won't get -1 and USHRT_MAX comparing equal.
>
Ok
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38046
