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Re: Two different Results between C and C++

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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.
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?

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Thread

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++ 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

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