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Groups > comp.lang.c > #104404
| From | Ben Bacarisse <ben.usenet@bsb.me.uk> |
|---|---|
| Newsgroups | comp.lang.c |
| Subject | Re: modifying local const variable run time |
| Date | 2017-02-22 21:55 +0000 |
| Organization | A noiseless patient Spider |
| Message-ID | <87h93l7ux1.fsf@bsb.me.uk> (permalink) |
| References | (3 earlier) <20170222173450.4fe314b3c852b242bb2dc35a@gmail.com> <idgrac1th0dk144r2niokdbstdc51ct8s9@4ax.com> <20170222175222.30c839c809d4d6c6b005274f@gmail.com> <o8kteq$hj3$1@dont-email.me> <35ac8d68-6fc3-4bc7-811d-2ab8a893c215@googlegroups.com> |
supercat@casperkitty.com writes:
<snip>
> There is another case where "const" is relevant: if a block starts with a
> declaration like
>
> void const * const restrict arbitraryName = &something;
>
> a compiler would be entitled to assume that the object in question will
> not be modified by any means during the execution of that block, even if
> the object in question is not const-qualified and might perfectly
> legitimately be modified *at times when the block isn't being executed*.
> That may facilitate optimizations that would not otherwise be possible,
> though it would seem like a directive that was equivalent to such a
> construct but didn't require defining a dummy variable might be
> clearer.
Is this an example of undefined behaviour you are describing:
int main(void)
{
int something = 1;
void const * const restrict arbitraryName = &something;
something = 0;
return something;
}
If so, can you say why it's undefined? I can see only one lvalue being
used (something) and a pointer to it (&something) is not an expression
based on arbitraryName. Have I misunderstood?
--
Ben.
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modifying local const variable run time rahul.dev.agg@gmail.com - 2017-02-22 06:39 -0800
Re: modifying local const variable run time GOTHIER Nathan <nathan.gothier@gmail.com> - 2017-02-22 16:06 +0100
Re: modifying local const variable run time rahul.dev.agg@gmail.com - 2017-02-22 07:26 -0800
Re: modifying local const variable run time David Brown <david.brown@hesbynett.no> - 2017-02-22 16:31 +0100
Re: modifying local const variable run time rahul.dev.agg@gmail.com - 2017-02-22 07:43 -0800
Re: modifying local const variable run time Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-02-22 16:06 +0000
Re: modifying local const variable run time James Kuyper <jameskuyper@verizon.net> - 2017-02-22 11:13 -0500
Re: modifying local const variable run time supercat@casperkitty.com - 2017-02-22 08:34 -0800
Re: modifying local const variable run time David Brown <david.brown@hesbynett.no> - 2017-02-22 23:03 +0100
Re: modifying local const variable run time GOTHIER Nathan <nathan.gothier@gmail.com> - 2017-02-22 17:34 +0100
Re: modifying local const variable run time Robert Wessel <robertwessel2@yahoo.com> - 2017-02-22 10:52 -0600
Re: modifying local const variable run time GOTHIER Nathan <nathan.gothier@gmail.com> - 2017-02-22 17:52 +0100
Re: modifying local const variable run time Keith Thompson <kst-u@mib.org> - 2017-02-22 09:33 -0800
Re: modifying local const variable run time James Kuyper <jameskuyper@verizon.net> - 2017-02-22 15:50 -0500
Re: modifying local const variable run time supercat@casperkitty.com - 2017-02-22 13:13 -0800
Re: modifying local const variable run time Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-02-22 21:55 +0000
Re: modifying local const variable run time supercat@casperkitty.com - 2017-02-22 14:43 -0800
Re: modifying local const variable run time Keith Thompson <kst-u@mib.org> - 2017-02-22 09:23 -0800
Re: modifying local const variable run time GOTHIER Nathan <nathan.gothier@gmail.com> - 2017-02-22 18:32 +0100
Re: modifying local const variable run time Keith Thompson <kst-u@mib.org> - 2017-02-22 09:50 -0800
Re: modifying local const variable run time David Brown <david.brown@hesbynett.no> - 2017-02-22 23:07 +0100
Re: modifying local const variable run time Keith Thompson <kst-u@mib.org> - 2017-02-22 15:20 -0800
Re: modifying local const variable run time David Brown <david.brown@hesbynett.no> - 2017-02-23 09:50 +0100
Re: modifying local const variable run time James Kuyper <jameskuyper@verizon.net> - 2017-02-22 10:16 -0500
Re: modifying local const variable run time Keith Thompson <kst-u@mib.org> - 2017-02-22 09:17 -0800
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