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Groups > comp.lang.c > #156909

Re: arranging items in a array with a sorted pointer-list

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Kaz Kylheku <563-365-8930@kylheku.com> writes:

> On 2020-12-01, Tim Rentsch <tr.17687@z991.linuxsc.com> wrote:
>
>> Kaz Kylheku <563-365-8930@kylheku.com> writes:
>>
>>> On 2020-12-01, Joe Pfeiffer <pfeiffer@cs.nmsu.edu> wrote:
>>>
>>>> Kaz Kylheku <563-365-8930@kylheku.com> writes:
>>>>
>>>>> It can be the case that at the time the cast is written, there is no
>>>>> const qualifier being cast away.  The accident occurs when someone
>>>>> later introduces const, and that cast now silently subverts it.
>>>>
>>>> Raising a question -- what would have been the downside (note that I'm
>>>> recognizing it's Too Late, just Monday morning quarterbacking), when
>>>> const was added to the language, to defining the cast so it doesn't
>>>> throw the const away?
>>>>
>>>> ie if you had a
>>>>
>>>>     const int x;
>>>>
>>>> and cast it with
>>>>     (char) x
>>>>
>>>> having x then treated as type
>>>>
>>>>     const char
>>>>
>>>> My immediate intuition is that there is no case in which one would want
>>>> to throw a const away with a cast, and this would have been a better
>>>> choice.
>>>>
>>>> Thoughts?
>>>
>>> I think that it would be a good choice for C++ or a C dialect
>>> inspired by C++, in which there are overloaded functions and other
>>> features.
>>>
>>> jhere is the problem that the current function
>>>
>>>   char *strchr(const char *str, int ch);
>>>
>>> could not be written in that dialect.  [...]
>>
>> Think again.  Yes it could.
>
> I don't see how it could be written in strictly-conforming code, as
> it can be now, without doing anything where the requirements are not
> defined, or at least unspecified or implementation-defined.

(In English usage, there is no hyphen between the adverb
"strictly" and the adjective "conforming".)

> I'm excluding possibilities such as:
>
>   char *strchr(const char *str, int ch)
>   {
>      union { char *y; const char *x; } u;
>
>      u.x = str;
>      return strchr_impl(u.y, ch);
>   }

There is no reason to exclude it.  The behavior is well defined,
and it produces the right result without having to depend on
behavior that is unspecified or implementation defined.

> I've thought about the memcpy hole:
>
>   char *strchr(const char *str, int ch)
>   {
>      char *uqstr;
>
>      memcpy(&uqstr, &str, sizeof uqstr);
>      return strchr_impl(uqsr, ch);
>   }
>
> In the memcpy call, the address of str is const char **, and that
> converts to the required const void *.  But does it?  Arguably, that
> conversion should arguably be banned under this dialect.  Reason being:
> it should be stipulated that pointer conversions must preserve const at
> the same level of indirection.  It can't just be that if the destination
> type has a const in it somewhere in he type tree, it's okay.
>
> I'm thinking in the context that goal of this dialect is to make it
> impossible to obtain a non-const-qualified pointer to any part of an
> object, given a const-qualified pointer to it, without doing anything
> erroneous or non-portable, where the requirements are not fastidiously
> well-defined.
>
> In that spirit, a conversion sequence like const char * -> intptr_t
> would also not be allowed in this dialect, because the const qualifier
> on the pointer must be preserved, and has nowhere to land in the target
> type, which has no matching indirection level.

I see.  I had thought you wanted to make a comment about C
except with a different rule for casting.  I see now that it was
just a lead-in to an exciting game of Calvinball.

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arranging items in a array with a sorted pointer-list Bonita Montero <Bonita.Montero@gmail.com> - 2020-11-28 11:00 +0100
  Re: arranging items in a array with a sorted pointer-list Melzzzzz <Melzzzzz@zzzzz.com> - 2020-11-28 10:49 +0000
    Re: arranging items in a array with a sorted pointer-list Bonita Montero <Bonita.Montero@gmail.com> - 2020-11-28 12:12 +0100
  Re: arranging items in a array with a sorted pointer-list Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2020-11-28 03:21 -0800
    Re: arranging items in a array with a sorted pointer-list Richard Damon <Richard@Damon-Family.org> - 2020-11-28 08:32 -0500
      Re: arranging items in a array with a sorted pointer-list Bonita Montero <Bonita.Montero@gmail.com> - 2020-11-28 14:49 +0100
        Re: arranging items in a array with a sorted pointer-list scott@slp53.sl.home (Scott Lurndal) - 2020-11-28 16:08 +0000
          Re: arranging items in a array with a sorted pointer-list Bonita Montero <Bonita.Montero@gmail.com> - 2020-11-28 17:16 +0100
          Re: arranging items in a array with a sorted pointer-list Bart <bc@freeuk.com> - 2020-11-28 16:23 +0000
            Re: arranging items in a array with a sorted pointer-list Bonita Montero <Bonita.Montero@gmail.com> - 2020-11-28 17:35 +0100
  Re: arranging items in a array with a sorted pointer-list "Alf P. Steinbach" <alf.p.steinbach+usenet@gmail.com> - 2020-11-28 17:34 +0100
    Re: arranging items in a array with a sorted pointer-list Bonita Montero <Bonita.Montero@gmail.com> - 2020-11-28 17:38 +0100
      Re: arranging items in a array with a sorted pointer-list Richard Damon <Richard@Damon-Family.org> - 2020-11-28 13:03 -0500
        Re: arranging items in a array with a sorted pointer-list Tim Woodall <news001@woodall.me.uk> - 2020-11-28 23:40 +0000
      Re: arranging items in a array with a sorted pointer-list Dolores Filandro <dolfiland8@gmail.com> - 2020-12-23 13:06 -0800
  Re: arranging items in a array with a sorted pointer-list Kaz Kylheku <563-365-8930@kylheku.com> - 2020-11-28 18:08 +0000
    Re: arranging items in a array with a sorted pointer-list Bonita Montero <Bonita.Montero@gmail.com> - 2020-11-28 19:14 +0100
      Re: arranging items in a array with a sorted pointer-list Kaz Kylheku <563-365-8930@kylheku.com> - 2020-11-28 19:14 +0000
  Re: arranging items in a array with a sorted pointer-list Tim Woodall <news001@woodall.me.uk> - 2020-11-28 18:13 +0000
  Re: arranging items in a array with a sorted pointer-list Siri Cruise <chine.bleu@yahoo.com> - 2020-11-28 17:16 -0800
    Re: arranging items in a array with a sorted pointer-list Juha Nieminen <nospam@thanks.invalid> - 2020-11-29 09:41 +0000
      Re: arranging items in a array with a sorted pointer-list Siri Cruise <chine.bleu@yahoo.com> - 2020-11-29 02:16 -0800
        Re: arranging items in a array with a sorted pointer-list Kaz Kylheku <563-365-8930@kylheku.com> - 2020-11-29 18:32 +0000
        Re: arranging items in a array with a sorted pointer-list Juha Nieminen <nospam@thanks.invalid> - 2020-11-30 09:01 +0000
          Re: arranging items in a array with a sorted pointer-list Ben Bacarisse <ben.usenet@bsb.me.uk> - 2020-11-30 13:03 +0000
            Re: arranging items in a array with a sorted pointer-list Kaz Kylheku <563-365-8930@kylheku.com> - 2020-11-30 20:46 +0000
              Re: arranging items in a array with a sorted pointer-list scott@slp53.sl.home (Scott Lurndal) - 2020-11-30 21:03 +0000
                Re: arranging items in a array with a sorted pointer-list Kaz Kylheku <563-365-8930@kylheku.com> - 2020-11-30 22:27 +0000
                Re: arranging items in a array with a sorted pointer-list Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2020-11-30 18:14 -0700
                Re: arranging items in a array with a sorted pointer-list James Kuyper <jameskuyper@alumni.caltech.edu> - 2020-11-30 23:02 -0500
                Re: arranging items in a array with a sorted pointer-list Dolores Filandro <dolfiland8@gmail.com> - 2020-11-30 20:12 -0800
                Re: arranging items in a array with a sorted pointer-list scott@slp53.sl.home (Scott Lurndal) - 2020-12-01 15:04 +0000
                Re: arranging items in a array with a sorted pointer-list Ben Bacarisse <ben.usenet@bsb.me.uk> - 2020-12-01 22:10 +0000
                Re: arranging items in a array with a sorted pointer-list Kaz Kylheku <563-365-8930@kylheku.com> - 2020-12-01 22:25 +0000
                Re: arranging items in a array with a sorted pointer-list Ben Bacarisse <ben.usenet@bsb.me.uk> - 2020-12-01 23:43 +0000
                Re: arranging items in a array with a sorted pointer-list James Kuyper <jameskuyper@alumni.caltech.edu> - 2020-12-01 23:25 -0500
                Re: arranging items in a array with a sorted pointer-list Ben Bacarisse <ben.usenet@bsb.me.uk> - 2020-12-02 14:53 +0000
                Re: arranging items in a array with a sorted pointer-list Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2020-12-02 07:03 -0800
                Re: arranging items in a array with a sorted pointer-list Ben Bacarisse <ben.usenet@bsb.me.uk> - 2020-12-02 23:48 +0000
                Re: arranging items in a array with a sorted pointer-list James Kuyper <jameskuyper@alumni.caltech.edu> - 2020-12-02 11:13 -0500
                Re: arranging items in a array with a sorted pointer-list Tim Rentsch <tr.17687@z991.linuxsc.com> - 2020-12-06 05:34 -0800
                Re: arranging items in a array with a sorted pointer-list Kaz Kylheku <563-365-8930@kylheku.com> - 2020-12-02 16:25 +0000
                Re: arranging items in a array with a sorted pointer-list Ben Bacarisse <ben.usenet@bsb.me.uk> - 2020-12-02 23:58 +0000
                Re: arranging items in a array with a sorted pointer-list Tim Rentsch <tr.17687@z991.linuxsc.com> - 2020-12-03 21:16 -0800
                Re: arranging items in a array with a sorted pointer-list Kaz Kylheku <563-365-8930@kylheku.com> - 2020-12-01 07:33 +0000
                Re: arranging items in a array with a sorted pointer-list Tim Rentsch <tr.17687@z991.linuxsc.com> - 2020-12-01 03:46 -0800
                Re: arranging items in a array with a sorted pointer-list Kaz Kylheku <563-365-8930@kylheku.com> - 2020-12-01 17:15 +0000
                Re: arranging items in a array with a sorted pointer-list Tim Rentsch <tr.17687@z991.linuxsc.com> - 2020-12-04 00:17 -0800
                Re: arranging items in a array with a sorted pointer-list Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2020-12-01 10:07 -0800
                Re: arranging items in a array with a sorted pointer-list Tim Rentsch <tr.17687@z991.linuxsc.com> - 2020-12-13 11:06 -0800
                Re: arranging items in a array with a sorted pointer-list Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2020-12-01 07:04 -0800
                Re: arranging items in a array with a sorted pointer-list Tim Rentsch <tr.17687@z991.linuxsc.com> - 2020-12-01 04:09 -0800
      Re: arranging items in a array with a sorted pointer-list Kaz Kylheku <563-365-8930@kylheku.com> - 2020-11-29 18:28 +0000
        Re: arranging items in a array with a sorted pointer-list dave_thompson_2@comcast.net - 2021-01-31 16:03 -0500
      Re: arranging items in a array with a sorted pointer-list Richard Damon <Richard@Damon-Family.org> - 2020-11-29 14:01 -0500
        Re: arranging items in a array with a sorted pointer-list Juha Nieminen <nospam@thanks.invalid> - 2020-11-30 09:05 +0000
          Re: arranging items in a array with a sorted pointer-list Richard Damon <Richard@Damon-Family.org> - 2020-11-30 07:09 -0500
          Re: arranging items in a array with a sorted pointer-list Ben Bacarisse <ben.usenet@bsb.me.uk> - 2020-11-30 13:06 +0000
            Re: arranging items in a array with a sorted pointer-list Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2020-11-30 06:28 -0800
              Re: arranging items in a array with a sorted pointer-list Ben Bacarisse <ben.usenet@bsb.me.uk> - 2020-11-30 15:50 +0000
            Re: arranging items in a array with a sorted pointer-list James Kuyper <jameskuyper@alumni.caltech.edu> - 2020-11-30 10:07 -0500
              Re: arranging items in a array with a sorted pointer-list Ben Bacarisse <ben.usenet@bsb.me.uk> - 2020-11-30 15:26 +0000
          Re: arranging items in a array with a sorted pointer-list James Kuyper <jameskuyper@alumni.caltech.edu> - 2020-11-30 10:02 -0500
    Re: arranging items in a array with a sorted pointer-list Ben Bacarisse <ben.usenet@bsb.me.uk> - 2020-11-29 12:32 +0000
      Re: arranging items in a array with a sorted pointer-list Tim Rentsch <tr.17687@z991.linuxsc.com> - 2020-11-29 18:58 -0800
    Re: arranging items in a array with a sorted pointer-list Bonita Montero <Bonita.Montero@gmail.com> - 2020-11-29 13:52 +0100
      Re: arranging items in a array with a sorted pointer-list Dolores Filandro <dolfiland8@gmail.com> - 2020-12-23 13:56 -0800
  Re: arranging items in a array with a sorted pointer-list Tim Rentsch <tr.17687@z991.linuxsc.com> - 2020-11-28 23:41 -0800
    Re: arranging items in a array with a sorted pointer-list Bonita Montero <Bonita.Montero@gmail.com> - 2020-12-05 12:23 +0100
      Re: arranging items in a array with a sorted pointer-list Tim Rentsch <tr.17687@z991.linuxsc.com> - 2020-12-06 16:27 -0800
        Re: arranging items in a array with a sorted pointer-list David Brown <david.brown@hesbynett.no> - 2020-12-07 11:17 +0100
  Re: arranging items in a array with a sorted pointer-list Kaz Kylheku <563-365-8930@kylheku.com> - 2020-11-29 18:34 +0000
    Re: arranging items in a array with a sorted pointer-list Bonita Montero <Bonita.Montero@gmail.com> - 2020-11-29 21:23 +0100
    Re: arranging items in a array with a sorted pointer-list Juha Nieminen <nospam@thanks.invalid> - 2020-11-30 09:10 +0000

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