Re: Two different Results between C and C++

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From	Tim Rentsch <tr.17687@z991.linuxsc.com>
Newsgroups	comp.lang.c
Subject	Re: Two different Results between C and C++
Date	Wed, 02 Sep 2020 23:00:36 -0700
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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:
>>
>> [...]
>>
>>>> All these statements are true, but none are particularly relevant.
>>>> You can construct an infinite number of valid C or C++ programs by
>>>> playing games with the grammar.  There are an infinite number of
>>>> legal C programs that use conditional operators nested 10,000
>>>> levels deep, but I doubt that any such programs exist in the wild
>>>> (except *maybe* as compiler capacity tests).  I think it's more
>>>> useful to look at actual code rather than contrived infinite sets
>>>> of programs.
>>>>
>>>> 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.
>>>
>>> This claim sounds like an article of faith, being offered without
>>> either proof or evidence.  If meant as just an empirical statement
>>> then of course there is no way anyone can know that.
>>
>> 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 statement was not an "article of faith".  It was somewhat
>> speculative.  I think it was correct, but it's not worth the effort
>> to perform a major research project to verify it.
>>
>> [...]
>
> 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.

Thread

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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