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Re: on why declare a struct with a single array in it

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Manfred <noname@add.invalid> writes:

> On 11/21/2021 9:51 PM, David Brown wrote:
>
>> On 21/11/2021 19:32, Manfred wrote:
>>
>>> On 11/21/2021 2:51 PM, David Brown wrote:
>>>
>>>> On 21/11/2021 02:44, Richard Damon wrote:
>>>>
>>>>> On 11/20/21 7:19 PM, Bart wrote:
>>>>>
>>>>>> It doesn't make sense.
>>>>
>>>> I don't want to make a habit of it, but I agree with Bart here :-)
>>>>
>>>>> Maybe not to you, but I would sure hate to have to keep track of all
>>>>> that data, and would likely just wrap this dumb malloc with something
>>>>> smarter.
>>>>
>>>> And that is /fine/. For those few cases where it might be inconvenient
>>>> to know the size at deallocation time, make a wrapper so that the size
>>>> is tracked.  If you need that functionality, write the code and pay the
>>>> price - others that don't need the heap to record their allocation sizes
>>>> shouldn't have to pay for your needs.  It is no different from malloc
>>>> and calloc - if you want the convenience of zeroing the memory, you can
>>>> use calloc, but if you don't want it you can use malloc and not pay for
>>>> the extra effort.
>>>>
>>>> Of course it is too late to make such untracked-size heap functions the
>>>> standard for C - I see it as an unlucky choice made long ago.  After
>>>> all, if you had "malloc_untracked" and "free_untracked" then it would be
>>>> a simple matter to implement traditional C "malloc" and "free" on top
>>>> of it.
>>>
>>> The problem I see with this is that it assumes one and only type of
>>> metadata information to be associated to the pointer, specifically the
>>> block size.
>>
>> No.  It merely relieves the heap implementation from having to store the
>> size of the allocation.  Any other metadata (such as for tracking free
>> space lists, or handling efficient multi-threaded access) will still be
>> needed.
>
> But it means that the implementation has to manage memory blocks based
> on size instead of something else - if it had to store anything else
> with the pointer, delegating the size to the programmer would be
> pointless
> One alternative that pops to mind is a pointer to the next block,
> however this might work, or nothing at all and a lookup table, or
> anything else I couldn't think of right now, since I am not designing
> the allocator, which the committee does not design either.
> I think it makes sense that the language defines the interface
> strictly to fulfill the requirements, and keep as much as possible of
> the design internal to the implementation.
>
> Moreover, the requested size (used by the user) may be different from
> the actual size (used by the allocator), which poses some consistency
> issues - but that's a side note.
>
>>> I believe there are countless implementations of malloc out there, and I
>>> guess this might not be the case, or it may be the case today but not
>>> tomorrow.
>>> The point is that if you set the interface to be pointer+size you also
>>> put constraints on the implementation, on top of the extra burden for
>>> the programmer.
>>
>> How could this suggestion impose any constraints on the implementation?
>>   The interface for getting the memory is the same (albeit with a
>> different name, in order to keep compatibility with existing code), and
>> the interface for freeing memory gives the implementation more
>> information.  It would be perfectly possible (though a little unhelpful)
>> for an implementation of the "_untracked" functions to be :
>>
>> 	#define malloc_untracked(size) malloc(size)
>> 	#define free_untracked(ptr, size) free(ptr)
>>
>> An implementation can do better, given this new information, but there
>> are no new limitations or restrictions.
>
> Well, requiring the programmer to keep track of the block size is a
> significant programming overhead - if it is unused, it's a significant
> waste I'd rather not pay for.

Anyone who seriously proposes having to supply a size argument to
free memory for a general purpose allocator like malloc() either
hasn't bothered to think or doesn't know how to think.  Kind of
par for the course for the long-running Bart and David show.

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on why declare a struct with a single array in it Meredith Montgomery <mmontgomery@levado.to> - 2021-11-12 15:48 -0300
  Re: on why declare a struct with a single array in it Guillaume <message@bottle.org> - 2021-11-12 19:56 +0100
    Re: on why declare a struct with a single array in it Ben Bacarisse <ben.usenet@bsb.me.uk> - 2021-11-12 19:31 +0000
      Re: on why declare a struct with a single array in it David Brown <david.brown@hesbynett.no> - 2021-11-12 21:07 +0100
        Re: on why declare a struct with a single array in it pozz <pozzugno@gmail.com> - 2021-11-18 15:53 +0100
          Re: on why declare a struct with a single array in it David Brown <david.brown@hesbynett.no> - 2021-11-18 16:13 +0100
            Re: on why declare a struct with a single array in it Manfred <noname@add.invalid> - 2021-11-18 16:26 +0100
              Re: on why declare a struct with a single array in it pozz <pozzugno@gmail.com> - 2021-11-18 17:22 +0100
                Re: on why declare a struct with a single array in it Manfred <noname@add.invalid> - 2021-11-18 18:04 +0100
                Re: on why declare a struct with a single array in it Meredith Montgomery <mmontgomery@levado.to> - 2021-11-19 16:00 -0300
                Re: on why declare a struct with a single array in it David Brown <david.brown@hesbynett.no> - 2021-11-18 22:58 +0100
                Re: on why declare a struct with a single array in it Guillaume <message@bottle.org> - 2021-11-19 17:53 +0100
                Re: on why declare a struct with a single array in it Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-11-19 11:27 -0800
                Re: on why declare a struct with a single array in it scott@slp53.sl.home (Scott Lurndal) - 2021-11-19 20:46 +0000
                Re: on why declare a struct with a single array in it Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-11-19 12:52 -0800
                Re: on why declare a struct with a single array in it David Brown <david.brown@hesbynett.no> - 2021-11-20 13:36 +0100
                Re: on why declare a struct with a single array in it Bart <bc@freeuk.com> - 2021-11-20 14:49 +0000
                Re: on why declare a struct with a single array in it Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-11-20 15:52 -0800
                Re: on why declare a struct with a single array in it Bart <bc@freeuk.com> - 2021-11-21 00:19 +0000
                Re: on why declare a struct with a single array in it Richard Damon <Richard@Damon-Family.org> - 2021-11-20 20:44 -0500
                Re: on why declare a struct with a single array in it David Brown <david.brown@hesbynett.no> - 2021-11-21 14:51 +0100
                Re: on why declare a struct with a single array in it Manfred <noname@add.invalid> - 2021-11-21 19:32 +0100
                Re: on why declare a struct with a single array in it David Brown <david.brown@hesbynett.no> - 2021-11-21 21:51 +0100
                Re: on why declare a struct with a single array in it Manfred <noname@add.invalid> - 2021-11-22 03:17 +0100
                Re: on why declare a struct with a single array in it David Brown <david.brown@hesbynett.no> - 2021-11-22 11:31 +0100
                Re: on why declare a struct with a single array in it Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2021-12-10 04:21 -0800
                Re: on why declare a struct with a single array in it David Brown <david.brown@hesbynett.no> - 2021-12-10 14:43 +0100
                Re: on why declare a struct with a single array in it Bart <bc@freeuk.com> - 2021-11-22 11:56 +0000
                Re: on why declare a struct with a single array in it Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-12-10 01:47 -0800
                Re: on why declare a struct with a single array in it Bart <bc@freeuk.com> - 2021-12-10 10:55 +0000
                Re: on why declare a struct with a single array in it David Brown <david.brown@hesbynett.no> - 2021-12-10 14:51 +0100
                Re: on why declare a struct with a single array in it Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-12-11 06:56 -0800
                Re: on why declare a struct with a single array in it Bart <bc@freeuk.com> - 2021-12-11 16:04 +0000
                Re: on why declare a struct with a single array in it Bart <bc@freeuk.com> - 2021-12-11 17:23 +0000
                Re: on why declare a struct with a single array in it Tim Rentsch <tr.17687@z991.linuxsc.com> - 2022-01-21 05:30 -0800
                Re: on why declare a struct with a single array in it Bart <bc@freeuk.com> - 2022-01-21 13:49 +0000
                Re: on why declare a struct with a single array in it "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2021-12-11 12:17 -0800
                Re: on why declare a struct with a single array in it gazelle@shell.xmission.com (Kenny McCormack) - 2021-12-12 13:00 +0000
                Re: on why declare a struct with a single array in it Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-12-12 08:25 -0800
                Re: on why declare a struct with a single array in it gazelle@shell.xmission.com (Kenny McCormack) - 2021-12-12 17:38 +0000
                Re: on why declare a struct with a single array in it Dick <thiebauddick2@aol.com> - 2021-12-12 16:19 -0500
                Re: on why declare a struct with a single array in it gazelle@shell.xmission.com (Kenny McCormack) - 2021-12-13 08:06 +0000
                Re: on why declare a struct with a single array in it Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2021-12-13 01:30 -0800
                Re: on why declare a struct with a single array in it David Brown <david.brown@hesbynett.no> - 2021-12-13 09:34 +0100
                Re: on why declare a struct with a single array in it Robert Latest <boblatest@yahoo.com> - 2021-12-13 18:53 +0000
                Re: on why declare a struct with a single array in it gazelle@shell.xmission.com (Kenny McCormack) - 2021-12-13 20:38 +0000
                Re: on why declare a struct with a single array in it Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-12-15 00:38 -0800
                Re: on why declare a struct with a single array in it gazelle@shell.xmission.com (Kenny McCormack) - 2021-12-15 11:21 +0000
                Re: on why declare a struct with a single array in it Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-12-15 10:26 -0800
                Re: on why declare a struct with a single array in it Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-12-15 10:45 -0800
                Re: on why declare a struct with a single array in it Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-12-10 10:52 -0800
                Re: on why declare a struct with a single array in it Guillaume <message@bottle.org> - 2021-11-22 04:06 +0100
                Re: on why declare a struct with a single array in it Bart <bc@freeuk.com> - 2021-11-22 11:32 +0000
                Re: on why declare a struct with a single array in it Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-11-22 13:00 -0800
                Re: on why declare a struct with a single array in it "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2021-11-21 13:08 -0800
                Re: on why declare a struct with a single array in it Richard Damon <Richard@Damon-Family.org> - 2021-11-20 20:44 -0500
                Re: on why declare a struct with a single array in it Bart <bc@freeuk.com> - 2021-11-21 12:22 +0000
                Re: on why declare a struct with a single array in it Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2021-11-20 20:13 -0700
                Re: on why declare a struct with a single array in it Bart <bc@freeuk.com> - 2021-11-21 12:35 +0000
                Re: on why declare a struct with a single array in it Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2021-11-21 10:53 -0700
                Re: on why declare a struct with a single array in it Bart <bc@freeuk.com> - 2021-11-21 18:49 +0000
                Re: on why declare a struct with a single array in it "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2021-11-21 13:04 -0800
                Re: on why declare a struct with a single array in it Bart <bc@freeuk.com> - 2021-11-21 14:42 +0000
                Re: on why declare a struct with a single array in it Guillaume <message@bottle.org> - 2021-11-21 01:34 +0100
                Re: on why declare a struct with a single array in it Bart <bc@freeuk.com> - 2021-11-21 00:48 +0000
                Re: on why declare a struct with a single array in it "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2021-11-20 16:58 -0800
                Re: on why declare a struct with a single array in it David Brown <david.brown@hesbynett.no> - 2021-11-21 14:40 +0100
                Re: on why declare a struct with a single array in it "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2021-11-21 12:59 -0800
                Re: on why declare a struct with a single array in it scott@slp53.sl.home (Scott Lurndal) - 2021-11-21 15:58 +0000
                Re: on why declare a struct with a single array in it gazelle@shell.xmission.com (Kenny McCormack) - 2021-11-20 10:55 +0000
  Re: on why declare a struct with a single array in it Jorgen Grahn <grahn+nntp@snipabacken.se> - 2021-11-13 08:47 +0000
    Re: on why declare a struct with a single array in it Guillaume <message@bottle.org> - 2021-11-13 18:23 +0100
  Re: on why declare a struct with a single array in it Kaz Kylheku <480-992-1380@kylheku.com> - 2021-11-13 17:55 +0000
  Re: on why declare a struct with a single array in it Anton Shepelev <anton.txt@g{oogle}mail.com> - 2021-11-19 13:14 +0300
    Re: on why declare a struct with a single array in it Meredith Montgomery <mmontgomery@levado.to> - 2021-11-19 16:07 -0300

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