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| From | David Brown <david.brown@hesbynett.no> |
|---|---|
| Newsgroups | comp.lang.c |
| Subject | Re: Mars lander crash |
| Date | 2016-12-11 23:42 +0100 |
| Organization | A noiseless patient Spider |
| Message-ID | <o2kkmj$fbj$1@dont-email.me> (permalink) |
| References | (5 earlier) <o2emds$5ek$1@dont-email.me> <o2epuf$juu$1@dont-email.me> <o2es0l$sea$1@dont-email.me> <o2jgbu$ih7$1@dont-email.me> <ln7f76utpn.fsf@kst-u.example.com> |
On 11/12/16 20:55, Keith Thompson wrote:
> David Brown <david.brown@hesbynett.no> writes:
> [...]
>> By now you must have realised that it is /impossible/ for C to have a
>> standard method of detecting integer overflows (and buffer overruns,
>> though these are new to the thread here). Please do not continue
>> arguing for them - it cannot and will not happen, and I believe you
>> already know this and understand some of the reasons for that (even if
>> you don't agree with all of the reasons).
>
> I don't know how you reached that conclusion.
>
> Standard C of course does not specify overflow checking. But leaving
> aside the question of whether it's a good idea, either a future C
> standard or a C implementation with extensions certainly could.
>
> As proof of concept, I present Ada. Ada has exceptions as a language
> feature, very similar to C++ exceptions. It also requires arithmetic
> operations to be checked, raising an exception if the result is out of
> range. (Ada also has modular types, similar to C unsigned types, with
> wraparound semantics.)
>
> For example, you might have:
>
> declare
> N: Integer := Integer'Last;
> begin
> N := N + 1;
> Put_Line("Overflow not detected");
> exception
> when Constraint_Error =>
> Put_Line("Overflow detected");
> end;
>
> and the program *must* print "Overflow detected" in a conforming
> implementation.
>
> Why do you think something similar (perhaps using signals rather than
> exceptions?) would be impossible in C?
>
See my answer to Ben on the same question. Basically, I think it is so
highly unrealistic that it would be put in the C standards that I used
the word "impossible". But that was an exaggeration.
A key difference here is that C++ and Ada have exceptions - C does not,
and I do not expect it ever to have exceptions. When a language /has/
exceptions, then it has a very suitable mechanism in place for handling
overflows like this.
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Re: Mars lander crash David Brown <david.brown@hesbynett.no> - 2016-12-11 18:57 +0100
Re: Mars lander crash jacobnavia <jacob@jacob.remcomp.fr> - 2016-12-11 19:23 +0100
Re: Mars lander crash David Brown <david.brown@hesbynett.no> - 2016-12-11 19:55 +0100
Re: Mars lander crash jacobnavia <jacob@jacob.remcomp.fr> - 2016-12-11 20:52 +0100
Re: Mars lander crash David Brown <david.brown@hesbynett.no> - 2016-12-11 23:37 +0100
Re: Mars lander crash supercat@casperkitty.com - 2016-12-11 16:10 -0800
Re: Mars lander crash BartC <bc@freeuk.com> - 2016-12-12 01:13 +0000
Re: Mars lander crash David Brown <david.brown@hesbynett.no> - 2016-12-12 09:53 +0100
Re: Mars lander crash supercat@casperkitty.com - 2016-12-12 08:30 -0800
Re: Mars lander crash David Brown <david.brown@hesbynett.no> - 2016-12-12 09:25 +0100
Re: Mars lander crash supercat@casperkitty.com - 2016-12-11 10:36 -0800
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Re: Mars lander crash jacobnavia <jacob@jacob.remcomp.fr> - 2016-12-11 18:53 +0100
Re: Mars lander crash Keith Thompson <kst-u@mib.org> - 2016-12-11 12:09 -0800
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Re: Mars lander crash jacobnavia <jacob@jacob.remcomp.fr> - 2016-12-11 23:02 +0100
Re: Mars lander crash Keith Thompson <kst-u@mib.org> - 2016-12-11 18:29 -0800
Re: Mars lander crash Keith Thompson <kst-u@mib.org> - 2016-12-11 12:03 -0800
Re: Mars lander crash Keith Thompson <kst-u@mib.org> - 2016-12-11 11:55 -0800
Re: Mars lander crash David Brown <david.brown@hesbynett.no> - 2016-12-11 23:42 +0100
Re: Mars lander crash Malcolm McLean <malcolm.mclean5@btinternet.com> - 2016-12-11 14:53 -0800
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Re: Mars lander crash supercat@casperkitty.com - 2016-12-09 08:43 -0800
Re: Mars lander crash Jerry Stuckle <jstucklex@attglobal.net> - 2016-12-09 09:47 -0500
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Re: Mars lander crash already5chosen@yahoo.com - 2016-12-09 05:53 -0800
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