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Re: Two different Results between C and C++

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Tiib <ootiib@hot.ee> writes:

I am sorry to have taken so long to respond to this posting.  My
apologies. 

> On Tuesday, 15 September 2020 15:01:22 UTC+3, Tim Rentsch  wrote:
>
>> Tiib <ootiib@hot.ee> writes:
>>
>>> All trouble that I have met was with undefined behaviors
>>> manifesting differently.
>>
>> What I think you mean is the only trouble that you know you have
>> met was undefined behavior manifesting differently.  But, since
>> you aren't sure about all the ways that semantics can vary
>> between C and C++, you don't know if there were other troubles.
>
> Yes.  I only know of my experience.  I can not know of experiences
> of someone else.  Defects are preferred to be discovered with
> testing but sometimes reach users.

My point is you don't know if the transformations tried resulted
in the same programs.  The last sentence there suggests that they
did not.

>>> Is there some real example of difficulties of translating
>>> semantics of C into semantics of common subset between C and
>>> C++?
>>
>> The question here is not whether some conversions are incredibly
>> difficult but whether most programs can be transformed with a
>> small effort.  If converting a program takes two months of full
>> time, even if the work is easy, that is not a small effort.
>
> Porting it has to provide benefits above alternatives and so it
> is important to predict it correctly.  Two man-months is certainly
> effort but relatively low effort in typical software projects.

I'm willing to take it for granted that a transformation is being
done because it is thought that some benefits will result.  The
question is not do the benefits justify the effort involved but
only how large an effort is needed.  Two months of full time is
not what I would call a small effort, regardless of how much
effort was needed on other parts of the project.

>>> My experience is that C++ compiler will lament about most places
>>> and additionally warn lot more.  The differences that I would
>>> search for manually (and if needed correct or made more explicit)
>>> are const variables linkage, inline functions linkage and usage of
>>> names of structs, unions and enums.  Then I would remove any
>>> pointless usage of size of character literals, logical operators,
>>> trues, falses and enums.  Finally if there is time then ... I
>>> would refactor away type punning with union despite all C++
>>> compilers seem to support it.  What else?  Sure it is work if we
>>> talk about lot of lines of code but easy work.
>>
>> What experience do you have actually trying to convert C code
>> into C++?  What can you say about the programs and types of
>> programs that were converted?  How long did it take in each case?
>> What evidence can you offer, if any, that the results you saw
>> would apply to all types of real-world programs and not just the
>> programs that you happened to work on?
>
> Sure I can talk about it but it is unsure how it helps as these
> are still just mine experiences.  There were different reasons in
> different projects.
>
> For example couple times there was desire to use certain C99 code
> bases of significant size on Windows, compiled with MSVC to
> integrate into larger Visual Studio project but to keep using
> same code on original equipment as well for not to fork code
> base into branches.  Microsoft's C compiler however was kind of
> C90 with some extensions.  Decided was that instead of back-porting
> C99 into that weird C90 it will be translated into common subset
> to be compilable with Visual C++.  Low amount of effort between
> other works.  Very common issues ... like that Visual C++
> did not yet support variadic macros so some tricks were loaned
> from Boost.Preprocessor that worked on both.  Or that some C++
> keyword like "new" was used as name.

This summary isn't very informative.  No quantitative statements
of how many projects, how much code was involved, or how long
each of the efforts took.  No indication of what kind of code was
being transformed, except that it used some C99 constructs, but
not which ones or how lightly/heavily.  (I should note that
variadic macros were given a specific mention.)

In reporting what the transformation entailed, you mention some
of the problems you found but not what was done (if anything)
to discover if there might have been other problems that did
not cause compilation errors.

> Whatever amount of experience can not show that it is guaranteed
> to be simple

Note that I am not looking for a guarantee, just some kind of
empirical evidence.

> but I don't have any idea what major difficulties there are
> supposed to be.

A key point.  If we don't know what all the problems are, we
can't say how large an effort is needed to address them.

> Common subset is only slightly crippled but fully useful as
> programming language and in those projects it was preferred to
> C90.

Point one:  preferred to C90 for those code bases.  Other code
bases may have reached different conclusions.

Point two:  whether the C++ version is preferred is irrelevant
to the question of how much effort is needed to accomplish the
transformation.

Point three:  because you don't know whether the conversion
efforts faithfully preserved program semantics, you actually
don't know if the "common subset" is indeed truly a common
subset.

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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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