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From: Eric Gallager <egall@gwmail.gwu.edu>
Date: Thu, 28 Apr 2022 08:02:28 -0400
Message-ID: <CAMfHzOv7v2V9Sax=rpGMQMcouaqXxhF+-BtNWdFdhNR=N=qo6A@mail.gmail.com>
Subject: Re: No type checking in ctype builtins
To: Jonathan Wakely <jwakely.gcc@gmail.com>
Cc: Andrea Monaco <andrea.monaco@autistici.org>,
 "gcc@gcc.gnu.org" <gcc@gcc.gnu.org>
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On Wed, Apr 27, 2022 at 12:20 PM Jonathan Wakely via Gcc
<gcc@gcc.gnu.org> wrote:
>
> On Wed, 27 Apr 2022 at 16:29, Andrea Monaco via Gcc <gcc@gcc.gnu.org> wrote:
> >
> >
> > This program
> >
> >   #include <ctype.h>
> >
> >   int main ()
> >   {
> >     char *s;
> >     isspace (s);
> >   }
> >
> > compiles with no warning in gcc 8.3.0, even though there's a type
> > mistake; the correct call would be isspace (*s).
>
> N.B. The correct call would be isspace((unsigned char)*s) because
> isspace has undefined behaviour if you pass it a char with a negative
> value.
>
> It would be nice if GCC warned about *that*.

Related bugs:
78155: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78155
99950: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99950