From: wempwer@gmail.com
To: Jonathan Wakely <jwakely.gcc@gmail.com>
Cc: gcc-help <gcc-help@gcc.gnu.org>
Subject: Re: how to make gcc warn about arithmetic signed overflow
Date: Sat, 21 Sep 2013 18:50:00 -0000 [thread overview]
Message-ID: <20130921185052.GG3086@a.lan> (raw)
In-Reply-To: <CAH6eHdQzJNQY4Meysi259RheSaGscKUF28OW43OvOD1rf6FkxQ@mail.gmail.com>
On Sat, Sep 21, 2013 at 07:30:02PM +0100, Jonathan Wakely wrote:
> On 21 September 2013 18:42, <wempwer@gmail.com> wrote:
> >
> > Hmm, I don't know too much about C++ but why would a C++ compiler
> > produce a warning only if two operands were const? I learned that in C
> > `const' modifier only means that I promise to the compiler that this
> > variable will be read-only,
>
> So the compiler knows that the values of ab and bc, because they must
> always have the values they were initialized with.
>
> If the compiler was smarter it would be able to also warn for
> non-const values if it can prove that nothing has modified the
> variables since they were initialized.
>
> > its value can be changed using pointers
>
> No, that's not true. You can't change the value of a const object in a
> valid program.
>
> > but the result is undefined and that const != constant expression.
I think I can but it may cause an undefined behavior:
const int bc = 50000;
int *p = &bc;
*p = 10;
printf("Modified const: %d\n", bc);
10 will be printed.
--
<wempwer@gmail.com>
next prev parent reply other threads:[~2013-09-21 18:50 UTC|newest]
Thread overview: 40+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-09-21 16:45 wempwer
2013-09-21 17:24 ` Jonathan Wakely
2013-09-21 17:41 ` wempwer
2013-09-21 18:30 ` Jonathan Wakely
2013-09-21 18:50 ` wempwer [this message]
2013-09-21 19:55 ` Jędrzej Dudkiewicz
2013-09-21 20:16 ` wempwer
2013-09-21 20:52 ` Jędrzej Dudkiewicz
2013-09-21 21:07 ` wempwer
2013-09-23 4:04 ` James K. Lowden
2013-09-23 7:55 ` Jonathan Wakely
2013-09-23 15:47 ` James K. Lowden
2013-09-23 21:50 ` Jonathan Wakely
2013-09-23 22:44 ` James K. Lowden
2013-09-23 23:20 ` Jonathan Wakely
2013-09-23 19:38 ` Dave Allured - NOAA Affiliate
2013-09-23 19:43 ` Oleg Endo
2013-09-23 20:37 ` Dave Allured - NOAA Affiliate
2013-09-23 19:48 ` Andrew Haley
2013-09-23 22:00 ` James K. Lowden
2013-09-24 17:48 ` Andrew Haley
2013-09-26 2:30 ` James K. Lowden
2013-09-26 8:29 ` Vincent Lefevre
2013-09-26 14:49 ` Andrew Haley
2013-09-26 17:03 ` Vincent Lefevre
2013-09-26 18:19 ` Andrew Haley
2013-09-27 7:58 ` Vincent Lefevre
2013-09-27 8:23 ` Andrew Haley
2013-09-27 9:28 ` Vincent Lefevre
2013-09-27 9:43 ` Andrew Haley
2013-09-26 17:41 ` Andrew Haley
2013-09-24 7:42 ` Brian Drummond
2013-09-21 17:53 ` Marc Glisse
2013-09-21 18:09 ` wempwer
2013-09-21 18:27 ` Jonathan Wakely
2013-09-21 19:32 ` wempwer
2013-09-22 15:52 ` Jonathan Wakely
2013-09-23 13:04 ` David Brown
2013-09-21 17:36 ` Brian Drummond
2013-09-21 17:45 ` wempwer
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