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Groups > comp.lang.c > #154924
| From | Tim Rentsch <tr.17687@z991.linuxsc.com> |
|---|---|
| Newsgroups | comp.lang.c |
| Subject | Re: Two different Results between C and C++ |
| Date | 2020-09-12 22:24 -0700 |
| Organization | A noiseless patient Spider |
| Message-ID | <86pn6q2qqy.fsf@linuxsc.com> (permalink) |
| References | (9 earlier) <a9597fac-1c3d-42bd-bbe4-b82a3d3d8816o@googlegroups.com> <86ft7x7j1h.fsf@linuxsc.com> <7abdc18a-78b6-4fb5-a7f7-82e6b220b389o@googlegroups.com> <86tuw85ocl.fsf@linuxsc.com> <83c9cb00-6c52-4837-95a2-6cfe31eb5d88o@googlegroups.com> |
Tiib <ootiib@hot.ee> writes:
> On Tuesday, 8 September 2020 17:34:58 UTC+3, Tim Rentsch wrote:
>
>> Tiib <ootiib@hot.ee> writes:
>>
>>> On Friday, 4 September 2020 16:45:16 UTC+3, Tim Rentsch wrote:
>>>
>>>> Tiib <ootiib@hot.ee> writes:
>>>>
>>>>> On Thursday, 3 September 2020 09:00:54 UTC+3, Tim Rentsch wrote:
>>>>>
>>>>>> Richard Damon <Richard@Damon-Family.org> writes:
>>>>>>
>>>>>>> On 6/21/20 2:40 PM, Keith Thompson wrote:
>>>>>>>
>>>>>>>> Tim Rentsch <tr.17687@z991.linuxsc.com> writes:
>>>>>>>>
>>>>>>>>> Keith Thompson <Keith.S.Thompson+u@gmail.com> writes:
>>
>> [..snipped for brevity.. blank lines may indicate snipping..]
>>
>>>>>>>>>> There are *some* programs that are legal C but not legal C++.
>>>>>>>>>> The most common causes of this are probably C++'s tighter
>>>>>>>>>> restrictions on implicit conversions involving void*, C code
>>>>>>>>>> that uses C++ keywords as identifiers, and C features that
>>>>>>>>>> haven't been incorporated into C++, such as VLAs, _Generic,
>>>>>>>>>> and compound literals. But almost all programs that are
>>>>>>>>>> legal C but not legal C++ can be made into legal C++ with a
>>>>>>>>>> small effort.
>>>>>>>>
>>>>>>>> When I wrote "almost all programs that are legal C but not
>>>>>>>> legal C++", I was referring to real-world programs, not the
>>>>>>>> infinite set of all possible programs. I probably could have
>>>>>>>> made that clearer.
>>>>>>>
>>>>>>> My experiance would be a bit different, most C programs from the
>>>>>>> 'wild' would likely fail as C++ precisely because of the
>>>>>>> implicit conversion from void* that does not happen in C++.
>>>>>>> These programs can trivially be converted to programs which are
>>>>>>> valid in both C and C++ by adding the explicit cast. [...]
>>>>>>
>>>>>> Lots of C programs fail as C++ because of constraint violations
>>>>>> or syntax errors. The problems are (obviously) easy to find,
>>>>>> and mostly I think easy to fix.
>>>>>>
>>>>>> The bigger problem is C code that is legal C++ but has different
>>>>>> semantics in C++ than in C. There are more of these than most
>>>>>> C or C++ developers think there are. I don't know anyone,
>>>>>> including myself, who can say with confidence that they know
>>>>>> all the different ways that source code can have a different
>>>>>> meaning in C++ compared to C.
>>>>>>
>>>>>> Clearly if someone doesn't know
>>>>>> what all the potential discrepancies are there is no way they
>>>>>> could find and fix them.
>>>>>
>>>>> In practice even developer who has never read neither standards
>>>>> nor that [diff.iso] can do it. There always are at least some
>>>>> tests. If test fails there is capability to figure it out why
>>>>> it fails. Once that capability has been applied to fix an issue
>>>>> also knowledge is obtained how to search for similar from
>>>>> untested parts of code.
>>>>
>>>> Testing can be used to show the presence of errors, but
>>>> never their absence. The code may seem to work even
>>>> when bugs are still lurking.
>>>>
>>>> Also, if a test fails, there is no guarantee we can track
>>>> down what caused the failure in any reasonably limited
>>>> amount of time. This is especially true when we don't
>>>> know what it is we're looking for.
>>>
>>> Yes, but so what? Writing code that can be compiled to produce
>>> close enough to be useful result on both C and C++ compilers is
>>> in practice about as difficult as to write code that produces
>>> close enough to be useful result on both clang and msvc.
>>>
>>> All programmers are usual humans and therefore fallible and so
>>> absence of errors in programs (including said compilers)
>>> is about as expensive (and about as unneeded) to achieve as
>>> collecting all berries of certain type from forest.
>>>
>>> It is just fact ... and that fact is easy to verify by looking at
>>> issue management systems of every large open source project that
>>> is happily used by millions of people. Lot of defects manifest as
>>> errors long time after these were introduced into code since these
>>> affect only tiny subset of users and even them very rarely.
>>>
>>> The idea of software development is to produce programs that
>>> are useful and help some people in something, not defect-free
>>> programs. That is also written so in license agreement of
>>> majority of software.
>>
>> The claim under discussion is two-fold (my wording, but I am
>> trying to be consistent with what Keith Thompson said above):
>>
>> (1) Any well-formed C program can be transformed into an
>> equivalent well-formed C program that is also a
>> well-formed, and equivalent, C++ program; and
>>
>> (2) For almost all "real-world" programs, to use Keith's
>> phrasing, such transformations can be effected with
>> a small effort.
>>
>> AFAICT your comments don't speak to either of these criteria.
>
> That depends on interpretation of these words. It is possible
> that I misinterpreted something there.
>
>> You seem to be arguing that it is possible, with some unspecified
>> amount of effort, to produce useful (even if not necessarily
>> equivalent) programs. What I'm talking about is only the
>> question of producing equivalent programs, and whether they can
>> be produced with a small effort. Do you see the difference
>> between that question and your comments above?
>
> You seem to ignore fact that very close to all "real world" programs
> are defective and so the equivalence isn't (and can't be) mathematical.
Of course it can be. There are lots of ways to transform a
program into a different program that has identical semantics,
whether or not the original program has defects. The transformed
program will then have exactly the same defects as the original.
Example: this declaration
int x = 1;
has exactly the same semantics as the transformed declaration
int x = (int) 1;
assuming of course there is no preprocessor funny business.
> Instead "equivalent" means "as useful for its usages".
I am using "equivalent" to mean "having exactly the same
semantics", which is also what I think Keith Thompson meant.
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Two different Results between C and C++ Real Troll <real.troll@trolls.com> - 2020-06-02 04:08 -1000
Re: Two different Results between C and C++ mark.bluemel@gmail.com - 2020-06-02 07:59 -0700
Re: Two different Results between C and C++ Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2020-06-02 09:26 -0700
Re: Two different Results between C and C++ Lew Pitcher <lew.pitcher@digitalfreehold.ca> - 2020-06-02 12:41 -0400
Re: Two different Results between C and C++ Ben Bacarisse <ben.usenet@bsb.me.uk> - 2020-06-02 18:09 +0100
Re: Two different Results between C and C++ Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2020-06-02 11:51 -0700
Re: Two different Results between C and C++ Ben Bacarisse <ben.usenet@bsb.me.uk> - 2020-06-02 20:44 +0100
Re: Two different Results between C and C++ Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2020-06-02 12:59 -0700
Re: Two different Results between C and C++ James Kuyper <jameskuyper@alumni.caltech.edu> - 2020-06-02 16:06 -0400
Re: Two different Results between C and C++ mark.bluemel@gmail.com - 2020-06-03 00:27 -0700
Re: Two different Results between C and C++ John Bode <jfbode1029@gmail.com> - 2020-06-02 08:41 -0700
Re: Two different Results between C and C++ Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2020-06-02 09:20 -0700
Re: Two different Results between C and C++ James Kuyper <jameskuyper@alumni.caltech.edu> - 2020-06-02 12:36 -0400
Re: Two different Results between C and C++ John Bode <jfbode1029@gmail.com> - 2020-06-02 11:39 -0700
Re: Two different Results between C and C++ Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2020-06-02 12:06 -0700
Re: Two different Results between C and C++ Richard Damon <Richard@Damon-Family.org> - 2020-06-02 15:41 -0400
Re: Two different Results between C and C++ Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2020-06-02 13:50 -0700
Re: Two different Results between C and C++ John Bode <jfbode1029@gmail.com> - 2020-06-04 13:16 -0700
Re: Two different Results between C and C++ James Kuyper <jameskuyper@alumni.caltech.edu> - 2020-06-04 16:41 -0400
Re: Two different Results between C and C++ Bonita Montero <Bonita.Montero@gmail.com> - 2020-09-08 16:54 +0200
Re: Two different Results between C and C++ Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2020-06-04 16:04 -0700
Re: Two different Results between C and C++ raltbos@xs4all.nl (Richard Bos) - 2020-06-04 20:47 +0000
Re: Two different Results between C and C++ James Kuyper <jameskuyper@alumni.caltech.edu> - 2020-06-04 17:35 -0400
Re: Two different Results between C and C++ raltbos@xs4all.nl (Richard Bos) - 2020-06-04 22:01 +0000
Re: Two different Results between C and C++ James Kuyper <jameskuyper@alumni.caltech.edu> - 2020-06-04 20:11 -0400
Re: Two different Results between C and C++ Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2020-06-04 16:10 -0700
Re: Two different Results between C and C++ Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2020-06-05 02:26 -0700
Re: Two different Results between C and C++ Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2020-06-05 11:33 -0700
Re: Two different Results between C and C++ Jorgen Grahn <grahn+nntp@snipabacken.se> - 2020-06-05 11:28 +0000
Re: Two different Results between C and C++ Tim Rentsch <tr.17687@z991.linuxsc.com> - 2020-06-21 00:53 -0700
Re: Two different Results between C and C++ Öö Tiib <ootiib@hot.ee> - 2020-06-21 03:57 -0700
Re: Two different Results between C and C++ Richard Damon <Richard@Damon-Family.org> - 2020-06-21 08:08 -0400
Re: Two different Results between C and C++ Tim Rentsch <tr.17687@z991.linuxsc.com> - 2020-06-28 04:59 -0700
Re: Two different Results between C and C++ James Kuyper <jameskuyper@alumni.caltech.edu> - 2020-06-21 10:59 -0700
Re: Two different Results between C and C++ Tim Rentsch <tr.17687@z991.linuxsc.com> - 2020-09-04 05:21 -0700
Re: Two different Results between C and C++ "james...@alumni.caltech.edu" <jameskuyper@alumni.caltech.edu> - 2020-09-05 13:02 -0700
Re: Two different Results between C and C++ Tim Rentsch <tr.17687@z991.linuxsc.com> - 2020-09-10 06:36 -0700
Re: Two different Results between C and C++ Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2020-09-10 12:03 -0700
Re: Two different Results between C and C++ Tim Rentsch <tr.17687@z991.linuxsc.com> - 2020-09-12 21:55 -0700
Re: Two different Results between C and C++ Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2020-06-21 11:40 -0700
Re: Two different Results between C and C++ Richard Damon <Richard@Damon-Family.org> - 2020-06-21 19:50 -0400
Re: Two different Results between C and C++ Tim Rentsch <tr.17687@z991.linuxsc.com> - 2020-09-02 23:00 -0700
Re: Two different Results between C and C++ Öö Tiib <ootiib@hot.ee> - 2020-09-03 09:57 -0700
Re: Two different Results between C and C++ David Brown <david.brown@hesbynett.no> - 2020-09-03 20:04 +0200
Re: Two different Results between C and C++ Tim Rentsch <tr.17687@z991.linuxsc.com> - 2020-09-04 06:44 -0700
Re: Two different Results between C and C++ Öö Tiib <ootiib@hot.ee> - 2020-09-05 06:51 -0700
Re: Two different Results between C and C++ Tim Rentsch <tr.17687@z991.linuxsc.com> - 2020-09-08 07:34 -0700
Re: Two different Results between C and C++ Öö Tiib <ootiib@hot.ee> - 2020-09-10 23:47 -0700
Re: Two different Results between C and C++ James Kuyper <jameskuyper@alumni.caltech.edu> - 2020-09-11 10:17 -0400
Re: Two different Results between C and C++ Öö Tiib <ootiib@hot.ee> - 2020-09-11 08:32 -0700
Re: Two different Results between C and C++ James Kuyper <jameskuyper@alumni.caltech.edu> - 2020-09-11 12:03 -0400
Re: Two different Results between C and C++ Öö Tiib <ootiib@hot.ee> - 2020-09-12 02:49 -0700
Re: Two different Results between C and C++ Tim Rentsch <tr.17687@z991.linuxsc.com> - 2020-09-12 22:24 -0700
Re: Two different Results between C and C++ Öö Tiib <ootiib@hot.ee> - 2020-09-13 06:25 -0700
Re: Two different Results between C and C++ Tim Rentsch <tr.17687@z991.linuxsc.com> - 2020-09-15 05:01 -0700
Re: Two different Results between C and C++ James Kuyper <jameskuyper@alumni.caltech.edu> - 2020-09-15 10:59 -0700
Re: Two different Results between C and C++ Öö Tiib <ootiib@hot.ee> - 2020-09-15 15:58 -0700
Re: Two different Results between C and C++ Tim Rentsch <tr.17687@z991.linuxsc.com> - 2020-12-28 21:38 -0800
Re: Two different Results between C and C++ Öö Tiib <ootiib@hot.ee> - 2020-12-30 05:39 -0800
Re: Two different Results between C and C++ James Kuyper <jameskuyper@alumni.caltech.edu> - 2020-09-03 12:46 -0700
Re: Two different Results between C and C++ Tim Rentsch <tr.17687@z991.linuxsc.com> - 2020-09-10 06:20 -0700
Re: Two different Results between C and C++ James Kuyper <jameskuyper@alumni.caltech.edu> - 2020-09-10 07:37 -0700
Re: Two different Results between C and C++ James Kuyper <jameskuyper@alumni.caltech.edu> - 2020-09-10 10:44 -0400
Re: Two different Results between C and C++ raltbos@xs4all.nl (Richard Bos) - 2020-06-29 16:20 +0000
Re: Two different Results between C and C++ Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2020-06-29 11:18 -0700
Re: Two different Results between C and C++ raltbos@xs4all.nl (Richard Bos) - 2020-06-29 21:46 +0000
Re: Two different Results between C and C++ Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2020-06-29 14:59 -0700
Re: Two different Results between C and C++ James Kuyper <jameskuyper@alumni.caltech.edu> - 2020-06-29 18:53 -0400
Re: Two different Results between C and C++ Sjouke Burry <burrynulnulfour@ppllaanneett.nnll> - 2020-06-30 01:40 +0200
Re: Two different Results between C and C++ Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2020-06-29 17:48 -0700
Re: Two different Results between C and C++ David Brown <david.brown@hesbynett.no> - 2020-06-30 07:45 +0200
Re: Two different Results between C and C++ James Kuyper <jameskuyper@alumni.caltech.edu> - 2020-06-30 15:11 -0400
Re: Two different Results between C and C++ Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2020-06-29 17:45 -0700
Re: Two different Results between C and C++ Tim Rentsch <tr.17687@z991.linuxsc.com> - 2020-09-04 03:13 -0700
Re: Two different Results between C and C++ Kaz Kylheku <793-849-0957@kylheku.com> - 2020-09-04 18:44 +0000
Re: Two different Results between C and C++ David Brown <david.brown@hesbynett.no> - 2020-09-05 15:57 +0200
Re: Two different Results between C and C++ Tim Rentsch <tr.17687@z991.linuxsc.com> - 2020-09-08 08:27 -0700
Re: Two different Results between C and C++ James Kuyper <jameskuyper@alumni.caltech.edu> - 2020-09-08 17:50 -0700
Re: Two different Results between C and C++ James Kuyper <jameskuyper@alumni.caltech.edu> - 2020-09-08 21:07 -0400
Re: Two different Results between C and C++ Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2020-09-08 18:28 -0700
Re: Two different Results between C and C++ James Kuyper <jameskuyper@alumni.caltech.edu> - 2020-09-08 22:14 -0400
Re: Two different Results between C and C++ Tim Rentsch <tr.17687@z991.linuxsc.com> - 2020-09-10 06:35 -0700
Re: Two different Results between C and C++ Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2020-09-04 11:46 -0700
Re: Two different Results between C and C++ Kaz Kylheku <793-849-0957@kylheku.com> - 2020-09-04 19:07 +0000
Re: Two different Results between C and C++ Tim Rentsch <tr.17687@z991.linuxsc.com> - 2020-09-10 04:15 -0700
Re: Two different Results between C and C++ Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2020-09-10 12:46 -0700
Re: Two different Results between C and C++ Tim Rentsch <tr.17687@z991.linuxsc.com> - 2020-12-06 16:49 -0800
Re: Two different Results between C and C++ James Kuyper <jameskuyper@alumni.caltech.edu> - 2020-06-02 15:51 -0400
Re: Two different Results between C and C++ Tim Rentsch <tr.17687@z991.linuxsc.com> - 2020-06-21 01:25 -0700
Re: Two different Results between C and C++ James Kuyper <jameskuyper@alumni.caltech.edu> - 2020-06-21 10:34 -0700
Re: Two different Results between C and C++ Tim Rentsch <tr.17687@z991.linuxsc.com> - 2020-09-04 06:38 -0700
Re: Two different Results between C and C++ "james...@alumni.caltech.edu" <jameskuyper@alumni.caltech.edu> - 2020-09-06 05:52 -0700
Re: Two different Results between C and C++ Tim Rentsch <tr.17687@z991.linuxsc.com> - 2020-09-10 06:37 -0700
Re: Two different Results between C and C++ Bonita Montero <Bonita.Montero@gmail.com> - 2020-09-08 16:54 +0200
Re: Two different Results between C and C++ Bonita Montero <Bonita.Montero@gmail.com> - 2020-09-08 16:52 +0200
Re: Two different Results between C and C++ Juha Nieminen <nospam@thanks.invalid> - 2020-06-02 18:45 +0000
Re: Two different Results between C and C++ Bart <bc@freeuk.com> - 2020-06-02 19:55 +0100
Re: Two different Results between C and C++ Lew Pitcher <lew.pitcher@digitalfreehold.ca> - 2020-06-02 15:11 -0400
Re: Two different Results between C and C++ Melzzzzz <Melzzzzz@zzzzz.com> - 2020-06-02 20:14 +0000
Re: Two different Results between C and C++ Lew Pitcher <lew.pitcher@digitalfreehold.ca> - 2020-06-02 16:19 -0400
Re: Two different Results between C and C++ Lew Pitcher <lew.pitcher@digitalfreehold.ca> - 2020-06-02 15:06 -0400
Re: Two different Results between C and C++ James Kuyper <jameskuyper@alumni.caltech.edu> - 2020-06-02 16:20 -0400
Re: Two different Results between C and C++ Pavel <pauldontspamtolk@removeyourself.dontspam.yahoo> - 2020-06-06 00:07 -0400
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