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Re: AVL tree insertion - programming exercise

From Kaz Kylheku <046-301-5902@kylheku.com>
Newsgroups comp.lang.c
Subject Re: AVL tree insertion - programming exercise
Date 2026-10-15 23:51 +0000
Organization A noiseless patient Spider
Message-ID <20261015163445.76@kylheku.com> (permalink)
References (1 earlier) <11amvh2$14pou$3@kst.eternal-september.org> <11ao2mr$4l9$1@reader2.panix.com> <11ap0fo$1t8gq$2@kst.eternal-september.org> <11aqnp0$sb$1@reader2.panix.com> <11arlj9$2q39c$1@kst.eternal-september.org>

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On 2026-10-15, Keith Thompson <Keith.S.Thompson+u@gmail.com> wrote:
> cross@spitfire.i.gajendra.net (Dan Cross) writes:
>> In article <11ap0fo$1t8gq$2@kst.eternal-september.org>,
>> Keith Thompson  <Keith.S.Thompson+u@gmail.com> wrote:
>>>cross@spitfire.i.gajendra.net (Dan Cross) writes:
>>>> In article <11amvh2$14pou$3@kst.eternal-september.org>,
>>>> Keith Thompson  <Keith.S.Thompson+u@gmail.com> wrote:
>>>>>[snip]
>>>>>So "a fundamental alignment requirement" and "size less than or equal
>>>>>to the size requested" are parallel requirements, both applying to
>>>>>the type of the pointed-to object.
>>>>
>>>> That is one of the two reasonable interpretations.  The other is
>>>> that the requirements placed on size and fundamental alignment
>>>> of the pointer type are cumulative and dependent on the size of
>>>> the allocation.  If so, then nothing in the C standard prevents
>>>> an implementation from from returning a pointer aligned to
>>>> `alignof(char)` for `malloc(1)`.
>>>
>>>I do see the parsing ambiguity now.
>>>
>>>I believe that's consistent with the way I parsed it.  A successful
>>>malloc(1) returns a value that can be assigned to a pointer of type
>>>char*, which points to the object type "char", which does have (a
>>>fundamental alignment requirement) and (a size less than or equal
>>>to the size requested).
>>
>> Right, but I think it's a bit deeper than that.
>>
>> Somewhat informally, the C17 wording could be read as requiring
>> that the pointer returned from `malloc` must be suitable for
>> assignment to any pointer to a type with `alignof(max_align_t)`
>> regardless of the requested size, which might be smaller.  N2293
>> calls this the, '"strong-alignment" reading.'
>
> The C17 wording is:
>
>     The pointer returned if the allocation succeeds is suitably aligned
>     so that it may be assigned to a pointer to any type of object with a
>     fundamental alignment requirement and then used to access such an
>     object or an array of such objects in the space allocated (until the
>     space is explicitly deallocated).

I suspect that this should be read as "any type of object which can
fit into the requested size".

> I don't see any other way to interpret that.

It can be interpreted a a defect.

Note that in a single sentence, the requirement is being given that:

- the pointer from a successful allocation is aligned for any object

- the pointer can be used to access such an object ... in the space
  allocated

From that we can infer that "any type" cannot literally be any type
Because if we have a successful malloc(1) and we choose "long long" to
be any type, the literally interpreted requirements are that we can
convert the pointer to "long long *" and use the resulting pointer for
access. That requires a malloc(1) to be adjusted to malloc(sizeof (long
long)); the requirement goes beyond alignment.

It must be that "any type" means "any type that can be
stored in the space allocated".

Then the whole thing makes sense; yes, the pointer can be converted
to that type and used to access such an object in the space allocated,
because it fits.

-- 
TXR Programming Language: http://nongnu.org/txr
Cygnal: Cygwin Native Application Library: http://kylheku.com/cygnal
Mastodon: @Kazinator@mstdn.ca

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Thread

AVL tree insertion - programming exercise Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-10-06 23:08 -0700
  Re: AVL tree insertion - programming exercise fir <profesor.fir@gmail.com> - 2026-10-07 15:25 +0200
    Re: AVL tree insertion - programming exercise Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-10-07 12:13 -0700
      Re: AVL tree insertion - programming exercise fir <profesor.fir@gmail.com> - 2026-10-07 21:28 +0200
        Re: AVL tree insertion - programming exercise Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-10-08 05:31 -0700
          Re: AVL tree insertion - programming exercise fir <profesor.fir@gmail.com> - 2026-10-09 11:12 +0200
            Re: AVL tree insertion - programming exercise fir <profesor.fir@gmail.com> - 2026-10-09 11:12 +0200
      Re: AVL tree insertion - programming exercise BGB <cr88192@gmail.com> - 2026-10-07 20:10 -0500
        Re: AVL tree insertion - programming exercise Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-10-08 05:56 -0700
          Re: AVL tree insertion - programming exercise BGB <cr88192@gmail.com> - 2026-10-08 15:09 -0500
            Re: AVL tree insertion - programming exercise fir <profesor.fir@gmail.com> - 2026-10-08 22:56 +0200
              Re: AVL tree insertion - programming exercise BGB <cr88192@gmail.com> - 2026-10-08 17:29 -0500
                Re: AVL tree insertion - programming exercise fir <profesor.fir@gmail.com> - 2026-10-09 09:56 +0200
            Re: AVL tree insertion - programming exercise Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2026-10-09 01:39 +0200
              Re: AVL tree insertion - programming exercise Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-10-09 00:03 -0700
            Re: AVL tree insertion - programming exercise Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-10-08 23:53 -0700
              Re: AVL tree insertion - programming exercise David Brown <david.brown@hesbynett.no> - 2026-10-09 10:34 +0200
                Re: AVL tree insertion - programming exercise Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2026-10-09 12:27 +0200
                Re: AVL tree insertion - programming exercise David Brown <david.brown@hesbynett.no> - 2026-10-09 12:59 +0200
                Re: AVL tree insertion - programming exercise bart <bc@freeuk.com> - 2026-10-09 11:43 +0100
                Re: AVL tree insertion - programming exercise David Brown <david.brown@hesbynett.no> - 2026-10-09 13:20 +0200
                Re: AVL tree insertion - programming exercise cross@spitfire.i.gajendra.net (Dan Cross) - 2026-10-09 12:38 +0000
                Re: AVL tree insertion - programming exercise David Brown <david.brown@hesbynett.no> - 2026-10-09 16:05 +0200
                Re: AVL tree insertion - programming exercise Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2026-10-09 17:54 +0200
                Re: AVL tree insertion - programming exercise Johann 'Myrkraverk' Oskarsson <johann@myrkraverk.invalid> - 2026-10-10 10:38 +0800
                Re: AVL tree insertion - programming exercise ram@zedat.fu-berlin.de (Stefan Ram) - 2026-10-10 03:12 +0000
                Re: AVL tree insertion - programming exercise Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-10-10 04:44 +0000
                Re: AVL tree insertion - programming exercise "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2026-10-10 14:12 -0700
                Re: AVL tree insertion - programming exercise cross@spitfire.i.gajendra.net (Dan Cross) - 2026-10-09 19:48 +0000
                Re: AVL tree insertion - programming exercise scott@slp53.sl.home (Scott Lurndal) - 2026-10-09 23:18 +0000
                Re: AVL tree insertion - programming exercise David Brown <david.brown@hesbynett.no> - 2026-10-10 15:27 +0200
                Re: AVL tree insertion - programming exercise cross@spitfire.i.gajendra.net (Dan Cross) - 2026-10-12 18:26 +0000
                Re: AVL tree insertion - programming exercise David Brown <david.brown@hesbynett.no> - 2026-10-12 21:17 +0200
                Re: AVL tree insertion - programming exercise Michael S <already5chosen@yahoo.com> - 2026-10-09 17:47 +0300
                Re: AVL tree insertion - programming exercise cross@spitfire.i.gajendra.net (Dan Cross) - 2026-10-09 16:48 +0000
                Re: AVL tree insertion - programming exercise Michael S <already5chosen@yahoo.com> - 2026-10-10 19:08 +0300
                Re: AVL tree insertion - programming exercise David Brown <david.brown@hesbynett.no> - 2026-10-10 18:29 +0200
                Re: AVL tree insertion - programming exercise cross@spitfire.i.gajendra.net (Dan Cross) - 2026-10-10 17:44 +0000
                Re: AVL tree insertion - programming exercise David Brown <david.brown@hesbynett.no> - 2026-10-10 23:22 +0200
                Re: AVL tree insertion - programming exercise cross@spitfire.i.gajendra.net (Dan Cross) - 2026-10-10 17:43 +0000
                Re: AVL tree insertion - programming exercise Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2026-10-10 20:35 +0200
                Re: AVL tree insertion - programming exercise cross@spitfire.i.gajendra.net (Dan Cross) - 2026-10-10 19:36 +0000
                Re: AVL tree insertion - programming exercise Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2026-10-10 22:08 +0200
                Re: AVL tree insertion - programming exercise Michael S <already5chosen@yahoo.com> - 2026-10-10 23:21 +0300
                Re: AVL tree insertion - programming exercise cross@spitfire.i.gajendra.net (Dan Cross) - 2026-10-10 20:55 +0000
                Re: AVL tree insertion - programming exercise scott@slp53.sl.home (Scott Lurndal) - 2026-10-10 20:22 +0000
                Re: AVL tree insertion - programming exercise Michael S <already5chosen@yahoo.com> - 2026-10-10 23:32 +0300
                Re: AVL tree insertion - programming exercise scott@slp53.sl.home (Scott Lurndal) - 2026-10-11 15:24 +0000
  Re: AVL tree insertion - programming exercise Bonita Montero <Bonita.Montero@gmail.com> - 2026-10-10 19:40 +0200
  Re: AVL tree insertion - programming exercise Andrey Tarasevich <noone@noone.net> - 2026-10-10 12:39 -0700
    Re: AVL tree insertion - programming exercise Michael S <already5chosen@yahoo.com> - 2026-10-10 23:00 +0300
    Re: AVL tree insertion - programming exercise Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2026-10-10 22:28 +0200
    Re: AVL tree insertion - programming exercise Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-10-10 19:02 -0700
  Re: AVL tree insertion - programming exercise "chine.bleu" <chine.bleu@yahoo.com> - 2026-10-13 01:38 -0700
    Re: AVL tree insertion - programming exercise David Brown <david.brown@hesbynett.no> - 2026-10-13 11:42 +0200
      Re: AVL tree insertion - programming exercise cross@spitfire.i.gajendra.net (Dan Cross) - 2026-10-13 10:55 +0000
      Re: AVL tree insertion - programming exercise Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-10-13 04:29 -0700
        Re: AVL tree insertion - programming exercise David Brown <david.brown@hesbynett.no> - 2026-10-13 14:01 +0200
          Re: AVL tree insertion - programming exercise Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-10-13 05:09 -0700
          Re: AVL tree insertion - programming exercise antispam@fricas.org (Waldek Hebisch) - 2026-10-13 19:01 +0000
        Re: AVL tree insertion - programming exercise cross@spitfire.i.gajendra.net (Dan Cross) - 2026-10-13 15:17 +0000
          Re: AVL tree insertion - programming exercise David Brown <david.brown@hesbynett.no> - 2026-10-13 17:39 +0200
          Re: AVL tree insertion - programming exercise Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-10-13 09:01 -0700
            Re: AVL tree insertion - programming exercise cross@spitfire.i.gajendra.net (Dan Cross) - 2026-10-13 21:17 +0000
              Re: AVL tree insertion - programming exercise "chine.bleu" <chine.bleu@yahoo.com> - 2026-10-13 18:01 -0700
              Re: AVL tree insertion - programming exercise Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-10-13 21:13 -0700
                Re: AVL tree insertion - programming exercise David Brown <david.brown@hesbynett.no> - 2026-10-14 09:43 +0200
                Re: AVL tree insertion - programming exercise cross@spitfire.i.gajendra.net (Dan Cross) - 2026-10-14 20:11 +0000
                Re: AVL tree insertion - programming exercise Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-10-14 15:25 -0700
                Re: AVL tree insertion - programming exercise David Brown <david.brown@hesbynett.no> - 2026-10-15 09:28 +0200
                Re: AVL tree insertion - programming exercise cross@spitfire.i.gajendra.net (Dan Cross) - 2026-10-14 14:13 +0000
                Re: AVL tree insertion - programming exercise Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2026-10-14 18:03 +0200
                Re: AVL tree insertion - programming exercise cross@spitfire.i.gajendra.net (Dan Cross) - 2026-10-14 18:21 +0000
                Re: AVL tree insertion - programming exercise Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-10-14 15:42 -0700
                Re: AVL tree insertion - programming exercise cross@spitfire.i.gajendra.net (Dan Cross) - 2026-10-15 14:25 +0000
                Re: AVL tree insertion - programming exercise Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-10-15 15:54 -0700
                Re: AVL tree insertion - programming exercise Kaz Kylheku <046-301-5902@kylheku.com> - 2026-10-15 23:51 +0000
                Re: AVL tree insertion - programming exercise Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-10-15 18:14 -0700
                Re: AVL tree insertion - programming exercise cross@spitfire.i.gajendra.net (Dan Cross) - 2026-10-16 03:09 +0000
                Re: AVL tree insertion - programming exercise Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-10-15 21:34 -0700
                Re: AVL tree insertion - programming exercise cross@spitfire.i.gajendra.net (Dan Cross) - 2026-10-16 11:27 +0000
                Re: AVL tree insertion - programming exercise Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-10-14 10:39 -0700
          Re: AVL tree insertion - programming exercise scott@slp53.sl.home (Scott Lurndal) - 2026-10-13 17:15 +0000
            Re: AVL tree insertion - programming exercise cross@spitfire.i.gajendra.net (Dan Cross) - 2026-10-13 21:30 +0000
      Re: AVL tree insertion - programming exercise "chine.bleu" <chine.bleu@yahoo.com> - 2026-10-13 08:19 -0700
      Re: AVL tree insertion - programming exercise "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2026-10-13 13:16 -0700
        Re: AVL tree insertion - programming exercise Michael S <already5chosen@yahoo.com> - 2026-10-13 23:28 +0300
    Re: AVL tree insertion - programming exercise James Kuyper <jameskuyper@alumni.caltech.edu> - 2026-10-13 06:20 -0400
      Re: AVL tree insertion - programming exercise cross@spitfire.i.gajendra.net (Dan Cross) - 2026-10-13 14:34 +0000
        Re: AVL tree insertion - programming exercise Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-10-13 20:45 -0700
          Re: AVL tree insertion - programming exercise cross@spitfire.i.gajendra.net (Dan Cross) - 2026-10-14 14:25 +0000
          Re: AVL tree insertion - programming exercise Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-10-14 20:54 -0700
            Re: AVL tree insertion - programming exercise Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-10-14 22:47 -0700
              Re: AVL tree insertion - programming exercise Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-10-15 04:42 -0700
              Re: AVL tree insertion - programming exercise "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2026-10-15 14:07 -0700
    Re: AVL tree insertion - programming exercise Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-10-13 03:52 -0700

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