Date: Tue, 10 Jun 2003 18:25:33 +0930 From: Malcolm Kay <malcolm.kay@internode.on.net> To: Sean Chittenden <sean@chittenden.org>, questions@freebsd.org Subject: Re: gcc me harder: -Wconversion bug? Message-ID: <200306101825.33674.malcolm.kay@internode.on.net> In-Reply-To: <20030609230324.GL65470@perrin.int.nxad.com> References: <20030609230324.GL65470@perrin.int.nxad.com>
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On Tue, 10 Jun 2003 08:33, Sean Chittenden wrote:
> [ Please CC: me on replies, not on questions@ ]
>
> Is this a GCC bug with the -Wconversion flag or am I doing something
> wrong? I know it's just a warning, but it's irritating me more than
> that dumb Dan Quayle quote, "if it weren't for that horse, I wouldn't
> have spent an extra year in college..." -sc
>
> % gcc -v
> Using built-in specs.
> Configured with: FreeBSD/i386 system compiler
> Thread model: posix
> gcc version 3.2.2 [FreeBSD] 20030205 (release)
> % uname -a
> FreeBSD hostname.example.com 5.1-CURRENT FreeBSD 5.1-CURRENT #2: Mon Jun 9
> 12:23:34 PDT 2003
> sean@hostname.example.com:/usr/src/sys/i386/compile/HOSTNAME i386
>
>
> % gcc -Wconversion test.c
> test.c: In function `main':
> test.c:5: warning: passing arg 1 of `f' with different width due to
> prototype
>
> /* Begin test.h */
> #ifndef __TEST_H__
> #define __TEST_H__
>
> #ifndef bool
> typedef char bool;
> #endif
>
> #ifndef true
> #define true ((bool)1)
> #endif
>
> #ifndef false
> #define false ((bool)0)
> #endif
>
> void f(bool b);
> #endif
> /* End test.h */
>
>
> /* Begin test.c */
> #include "test.h"
>
> int
> main(void) {
> f(true);
> return(0);
> }
>
> void
> f(bool b) { }
> /* End test.c */
It seems to me that this is doing exactly what is claimed for -Wconversion.
To quote from the gcc man page:
-Wconversion
Warn if a prototype causes a type conversion that
is different from what would happen to the same ar-
gument in the absence of a prototype. ...
Now in the absence of a prototype for f() the argument true would be promoted
from char/bool to int before being passed to the function. With the prototype
in scope it is not promoted. Different argument widths so warning delivered.
Malcolm
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