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

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Joe Pfeiffer <pfeiffer@cs.nmsu.edu> writes:

> 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?

1. Presumably you mean it for pointer types, so a (T*) cast of a
   (const X*) value would result in a (const T*) value.  There is
   effectively no difference between (char) x and (const char) x.

2. It violates the Law of Least Astonishment.

3. There are cases where throwing away 'const' at the start of a
   pointer type is useful.  Functions in the standard library do
   it;  as it happens I ran into a case recently where casting
   away 'const' from a pointer type looks like a good way to
   handle something that came up in code I am working on.

4. If someone wants a const-preserving pointer cast, it can be
   done in C11 and later, using _Generic:


        #define CONST_PRESERVING_CAST( T, p ) (         \
            _Generic( 0 ? (p) : (void*) (p),            \
                const void * : (const T)(p),            \
                      void * : (T)(p)                   \
            )                                           \
        )

        void
        example(){
            const int ci;
            int *p = CONST_PRESERVING_CAST( int *, &ci );
            // Produces an error.  To fix the error,
            // either remove 'const' from 'ci' type,
            // or add 'const' to start of 'p' type.
        }

I admit the macro isn't perfect, but it should be possible to
adapt it to other use cases where those may be important.

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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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