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Groups > comp.lang.c > #163544
| From | Bart <bc@freeuk.com> |
|---|---|
| Newsgroups | comp.lang.c |
| Subject | Re: on why declare a struct with a single array in it |
| Date | 2021-11-21 12:22 +0000 |
| Organization | A noiseless patient Spider |
| Message-ID | <snddlt$684$1@dont-email.me> (permalink) |
| References | (12 earlier) <874k87q35r.fsf@nosuchdomain.example.com> <snaq53$voh$1@dont-email.me> <875ysmjsfz.fsf@nosuchdomain.example.com> <snc3a0$6gs$1@dont-email.me> <LvhmJ.55057$np6.17637@fx46.iad> |
On 21/11/2021 01:44, Richard Damon wrote: > On 11/20/21 7:19 PM, Bart wrote: >> On 20/11/2021 23:52, Keith Thompson wrote: >>> David Brown <david.brown@hesbynett.no> writes: >>>> On 19/11/2021 21:52, Keith Thompson wrote: >>> [...] >>>>> 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. >>> >>> Meh. That would have introduced another rich source of programming >>> errors (passing the wrong size). >> >> You could also pass the wrong size to malloc, or the wrong pointer to >> free. >> >>> Probably most implementations would >>> have kept track of the size anyway, so they could detect errors. >> >> I doubt that, unless it's for debugging mode. >> >> If an application needs to allocate 100 million 32-byte nodes, which >> would occupy 3.2GB by themselves, how much extra would be needed for >> the size, 'just for checking'? >> >> On my machine that seems to be 16 bytes per node, so 50% more. 1.6GB >> extra just so someone can write: >> >> free(p); >> >> instead of: >> >> free(p, sizeof(treenode)); >> >> possibly in just one place in the program. >> >> It doesn't make sense. >> > > 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. I still don't understand why you have to keep track of /allocated/ blocks. Once allocated, they belong to the application; why does the allocator need to care about them? Once deallocated, or before they are allocated, then the allocator can do what it likes with them. But it can use data within the blocks: it doesn't need any extra space. (Unless the block is tiny, like one byte, then it will have to impose a minimum size.) > If you need a lot of a fixed sized blocks, there are lots of algorithms > that work well for that with much less or zero overhead (if the blocks > are big enough for a pointer) Lots of same-sized blocks you mean? Then sure, there are all sorts of custom allocators that could be used. Including the case where you know that you will never free memory so there is no point wasting time and space with housekeeping information. But this is about the general purpose allocator provided by with malloc and free. You can always add a 'better' allocator on top that uses extra overheads; it's harder the other way around.
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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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