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Date: Fri, 08 Oct 2004 18:24:00 -0000
From: Jamie Lokier <jamie@shareable.org>
To: Joe Buck <Joe.Buck@synopsys.com>
Cc: Nick Ing-Simmons <nick@ing-simmons.net>, gcc@gcc.gnu.org,
   "'Morten Welinder'" <terra@gnome.org>, Dave Korn <dk@artimi.com>
Subject: Re: signed vs unsigned pointer warning
Message-ID: <20041008172801.GB13758@mail.shareable.org>
References: <20040922161751.B4F6A1422D53@darter.rentec.com> <NUTMEGODkUqESudbgsy00000021@NUTMEG.CAM.ARTIMI.COM> <20040926192142.GA29842@mail.shareable.org> <20040926192142.GA29842@mail.shareable.org> <20041008130623.9516.4@llama.elixent.com> <20041008091714.A1695@synopsys.com> <m3d5zttbu6.fsf@multivac.cwru.edu> <20041008100853.A2207@synopsys.com>
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Joe Buck wrote:
> No, (unsigned)-1 does not turn into 255, it turns into a very large
> number.  You cannot store EOF in a char.  Here's a bug fix:
> 
> 	 table_lookup[1U+(unsigned)(c)]
> 
> Now EOF goes into slot 0.

The trouble is that char 255 (or char -1 depending on your point of
view) _might_ also go into slot 0, depending on the type of c and how
it was passed.

Do the standards require anything about the result of is*(EOF), or do
the functions simply have to accept that as an argument?

In any case, code which writes:

    char c = ... ;
    ...
    if (isspace(c)) {
        ...
    }

Surely deserves a warning from the compiler, just because it'll fail
on some OSes.

-- Jamie