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Date: Mon, 07 Mar 2011 14:20:00 -0000
Message-ID: <AANLkTimswZGhUmdEnqz2Mgp+V6ENCLK2CJisSwCsSfbp@mail.gmail.com>
Subject: Re: Warning using -Wconversion and -Ox in gcc 4.5 and 4.6 but not in previous releases
From: =?ISO-8859-1?Q?Jos=E9_Luis_Garc=EDa_Pallero?= <jgpallero@gmail.com>
To: gcc-help@gcc.gnu.org
Cc: Marc Glisse <marc.glisse@inria.fr>
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El d=EDa 7 de marzo de 2011 14:16, Marc Glisse <marc.glisse@inria.fr> escri=
bi=F3:
> On Mon, 7 Mar 2011, Jos=E9 Luis Garc=EDa Pallero wrote:
>
>> Hello,
>> In this example:
>>
>> #include<stdlib.h>
>> #include<string.h>
>> int main() {
>> =A0 strspn("hello","h");
>> =A0 return 0;
>> }
>>
>> I obtain a warning as:
>>
>> test.c:4:5: warning: conversion to =91size_t=92 from =91int=92 may chang=
e the
>> sign of the result
>>
>> If I compile the program with the options:
>>
>> gcc -Wconversion -O test.c -o test
>
> Note that your example can be reduced to:
> int main() {
> =A0 =A0 =A0 =A0(0 ? ((void) (0), 0) : 1u) ;
> =A0 =A0 =A0 =A0return 0;
> }
>
> Not a most useful warning indeed...
>
>> The warning appears with -O, -O1, -O2 and -O3, but not with -O0.
>
> glibc includes different code when __OPTIMIZE__ is defined.
>
> --
> Marc Glisse
>

But why in previous gcc versions the warning didn't appears. And
strspn() is a common function in string.h. I don't understand why the
call to strspn() with correct arguments emits a warning.

--=20
*****************************************
Jos=E9 Luis Garc=EDa Pallero
jgpallero@gmail.com
(o<
/ / \
V_/_
Use Debian GNU/Linux and enjoy!
*****************************************