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Groups > comp.lang.c > #163523
| From | Bart <bc@freeuk.com> |
|---|---|
| Newsgroups | comp.lang.c |
| Subject | Re: on why declare a struct with a single array in it |
| Date | 2021-11-20 14:49 +0000 |
| Organization | A noiseless patient Spider |
| Message-ID | <snb1u4$ppq$1@dont-email.me> (permalink) |
| References | (9 earlier) <sn8kq9$tep$1@gioia.aioe.org> <87czmwosiq.fsf@nosuchdomain.example.com> <Y2UlJ.79170$ya3.75666@fx38.iad> <874k87q35r.fsf@nosuchdomain.example.com> <snaq53$voh$1@dont-email.me> |
On 20/11/2021 12:36, David Brown wrote:
> On 19/11/2021 21:52, Keith Thompson wrote:
>> scott@slp53.sl.home (Scott Lurndal) writes:
>>> Keith Thompson <Keith.S.Thompson+u@gmail.com> writes:
>>>> Guillaume <message@bottle.org> writes:
>>>>> Le 18/11/2021 à 22:58, David Brown a écrit :
>>>
>>>>> Now there are kind of exceptions to that, but that are purely
>>>>> "hand-implemented" and have nothing to do with the language itself:
>>>>> for instance, the typical malloc() behavior. Behind the scenes,
>>>>> pointers returned by malloc() are "fat pointers", and you can also
>>>>> implement your own fat pointers if you so wish. But the language
>>>>> doesn't care. It has no provision for that, except you can do pointer
>>>>> arithmetics to your heart's content.
>>>>
>>>> I'm not sure what you mean about malloc() returning "fat pointers".
>>>> malloc() returns a void* with no information about the size or type of
>>>> what it points to. Some implementations might provide a way to query
>>>> the size of the allocated space, but that's not standard.
>>>
>>> Many malloc implementations reserve additional space, either before
>>> or after the allocated space for bookkeeping and alignment purposes.
>>>
>>> Perhaps that is the source of Guillaume's "fat pointer" reference.
>>
>> Perhaps -- but typically that information is not stored in the pointer
>> itself. If it were, all void* values would have to store that extra
>> information.
>>
>> (I think it's easier to store bookkeeping data before the allocated
>> space. If you store it after the space, it's hard to know where it is.)
>>
>
> That's the most common way for a simple malloc/free system.
>
> It has always struck me as a mistake that C did things that way - in my
> opinion, "free" should have taken an additional parameter of the size
> for the deallocation.
Yeah, that's how I always implemented deallocations in the days when I
had to code everthing.
I was suprised when I first came across C's free which magically didn't
need that info!
Rather an indulgence for a lower level systems language.
When I go to some pains to allocate a block of exactly 4096 bytes, I
expect the next 4096-byte block to follow immediately, not be offset
from it by 4, 8 or 28 bytes or however it decides to do it.
Worse if my block is only 8 or 16 bytes:
for (int i=0; i<10; ++i) {
p=malloc(8);
printf("%d\n",(int)p);
}
The first three compilers I tried (I think all using msvcrt), used 32
bytes per allocation. 300% overhead!
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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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