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| From | Keith Thompson <kst-u@mib.org> |
|---|---|
| Newsgroups | comp.lang.c |
| Subject | Re: Padding involved |
| Date | 2014-03-07 16:24 -0800 |
| Organization | None to speak of |
| Message-ID | <lnr46dv8ol.fsf@nuthaus.mib.org> (permalink) |
| References | <43b13d99-38eb-4711-824d-5fc40d55edf3@googlegroups.com> <lfddjo$5gp$1@dont-email.me> <54bf1188-f3d7-409f-a15a-522cb3038333@googlegroups.com> <lfdjmp$jmh$1@dont-email.me> <602c31f6-8abb-4ddb-b64a-4c681c404659@googlegroups.com> |
anish kumar <yesanishhere@gmail.com> writes:
[...]
> Understood. How about below:
> int main(void) {
> struct test {
> char a;
> int b;
> short c;
> };
> printf("%d\n", sizeof(struct test));
> return 0;
> }
> I completely understand what will be the size of the struct with and
> without mapping but the question is what parameters decides the padding
> involved? Such as size of registers or size of address/data bus of the
> processor?
One more nitpick: sizeof yields a result of type size_t; the "%d"
format requires an argument of type int. Use the "%zu" format, or
convert the sizeof result to int (or to unsigned long and use "%lu").
The amount of padding is determined by the alignment requirement
for each member type. The amount of padding at the end is also
influenced by the maximum alignment requirement for any member.
And there might be an additional alignment requirement for the
structure as a whole.
Alignment requirements are, to some extent, up to whim of the
compiler developers, but typically they're determined by an ABI
for a given platform. On some CPUs misaligned accesses (e.g.,
reading or writing a 4-byte integer at an odd address) are merely
slower than aligned accesses; on others they can crash your program
(or, worse, quietly give you incorrect results).
The comp.lang.c FAQ is at http://www.c-faq.com/; question 2.12
discusses structure padding.
--
Keith Thompson (The_Other_Keith) kst-u@mib.org <http://www.ghoti.net/~kst>
Working, but not speaking, for JetHead Development, Inc.
"We must do something. This is something. Therefore, we must do this."
-- Antony Jay and Jonathan Lynn, "Yes Minister"
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Padding involved anish singh <anish198519851985@gmail.com> - 2014-03-07 13:13 -0800
Re: Padding involved jacob navia <jacob@spamsink.net> - 2014-03-07 22:17 +0100
Re: Padding involved Eric Sosman <esosman@comcast-dot-net.invalid> - 2014-03-07 16:26 -0500
Re: Padding involved anish singh <anish198519851985@gmail.com> - 2014-03-07 13:49 -0800
Re: Padding involved Eric Sosman <esosman@comcast-dot-net.invalid> - 2014-03-07 18:11 -0500
Re: Padding involved anish kumar <yesanishhere@gmail.com> - 2014-03-07 15:19 -0800
Re: Padding involved Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2014-03-07 16:26 -0700
Re: Padding involved anish kumar <yesanishhere@gmail.com> - 2014-03-07 15:41 -0800
Re: Padding involved James Kuyper <jameskuyper@verizon.net> - 2014-03-07 18:50 -0500
Re: Padding involved glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2014-03-08 00:10 +0000
Re: Padding involved Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2014-03-08 09:27 -0700
Re: Padding involved Keith Thompson <kst-u@mib.org> - 2014-03-07 16:24 -0800
Re: Padding involved anish kumar <yesanishhere@gmail.com> - 2014-03-07 16:45 -0800
Re: Padding involved Kaz Kylheku <kaz@kylheku.com> - 2014-03-08 01:03 +0000
Re: Padding involved David Thompson <dave.thompson2@verizon.net> - 2014-03-28 06:11 -0400
Re: Padding involved glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2014-03-28 18:45 +0000
Re: Padding involved James Kuyper <jameskuyper@verizon.net> - 2014-03-28 15:23 -0400
Re: Padding involved Keith Thompson <kst-u@mib.org> - 2014-03-28 12:40 -0700
Re: Padding involved glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2014-03-28 21:19 +0000
Re: Padding involved Stephen Sprunk <stephen@sprunk.org> - 2014-03-28 17:07 -0500
Re: Padding involved Eric Sosman <esosman@comcast-dot-net.invalid> - 2014-03-28 18:25 -0400
Re: Padding involved Stephen Sprunk <stephen@sprunk.org> - 2014-03-28 21:15 -0500
Re: Padding involved Keith Thompson <kst-u@mib.org> - 2014-03-29 01:03 -0700
Re: Padding involved Tim Rentsch <txr@alumni.caltech.edu> - 2014-03-29 14:23 -0700
Re: Padding involved glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2014-03-30 01:43 +0000
Re: Padding involved James Kuyper <jameskuyper@verizon.net> - 2014-03-28 21:32 -0400
Re: Padding involved Richard Damon <Richard@Damon-Family.org> - 2014-03-28 21:59 -0400
Re: Padding involved Stephen Sprunk <stephen@sprunk.org> - 2014-03-29 00:46 -0500
Re: Padding involved James Kuyper <jameskuyper@verizon.net> - 2014-03-29 08:51 -0400
Re: Padding involved Eric Sosman <esosman@comcast-dot-net.invalid> - 2014-03-29 08:57 -0400
Re: Padding involved Stephen Sprunk <stephen@sprunk.org> - 2014-03-30 18:53 -0500
Re: Padding involved Eric Sosman <esosman@comcast-dot-net.invalid> - 2014-03-30 20:25 -0400
Re: Padding involved Stephen Sprunk <stephen@sprunk.org> - 2014-03-31 11:34 -0500
Re: Padding involved Keith Thompson <kst-u@mib.org> - 2014-03-31 11:27 -0700
Re: Padding involved Keith Thompson <kst-u@mib.org> - 2014-03-31 11:36 -0700
Re: Padding involved Kaz Kylheku <kaz@kylheku.com> - 2014-03-31 19:14 +0000
Re: Padding involved Stephen Sprunk <stephen@sprunk.org> - 2014-03-31 15:43 -0500
Re: Padding involved Phil Carmody <thefatphil_demunged@yahoo.co.uk> - 2014-04-01 03:12 +0300
Re: Padding involved Stephen Sprunk <stephen@sprunk.org> - 2014-04-03 00:45 -0500
Re: Padding involved Stephen Sprunk <stephen@sprunk.org> - 2014-03-29 13:02 -0500
Re: Padding involved Eric Sosman <esosman@comcast-dot-net.invalid> - 2014-03-29 14:44 -0400
Re: Padding involved glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2014-03-29 19:49 +0000
Re: Padding involved James Kuyper <jameskuyper@verizon.net> - 2014-03-30 19:12 -0400
Re: Padding involved Stephen Sprunk <stephen@sprunk.org> - 2014-03-31 16:20 -0500
Re: Padding involved James Kuyper <jameskuyper@verizon.net> - 2014-03-31 17:53 -0400
Re: Padding involved Phil Carmody <thefatphil_demunged@yahoo.co.uk> - 2014-04-01 03:22 +0300
Re: Padding involved Stephen Sprunk <stephen@sprunk.org> - 2014-04-04 14:36 -0500
Re: Padding involved James Kuyper <jameskuyper@verizon.net> - 2014-04-04 17:33 -0400
Re: Padding involved Tim Rentsch <txr@alumni.caltech.edu> - 2014-04-14 13:46 -0700
Re: Padding involved glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2014-04-14 22:00 +0000
Re: Padding involved Keith Thompson <kst-u@mib.org> - 2014-04-14 15:37 -0700
Re: Padding involved Tim Rentsch <txr@alumni.caltech.edu> - 2014-04-17 09:11 -0700
Re: Padding involved Tim Rentsch <txr@alumni.caltech.edu> - 2014-04-14 13:25 -0700
Re: Padding involved Keith Thompson <kst-u@mib.org> - 2014-03-29 00:57 -0700
Re: Padding involved James Kuyper <jameskuyper@verizon.net> - 2014-03-29 08:57 -0400
Re: Padding involved Keith Thompson <kst-u@mib.org> - 2014-03-29 14:18 -0700
Re: Padding involved Tim Rentsch <txr@alumni.caltech.edu> - 2014-03-30 12:02 -0700
Re: Padding involved Keith Thompson <kst-u@mib.org> - 2014-03-30 19:35 -0700
Re: Padding involved Tim Rentsch <txr@alumni.caltech.edu> - 2014-04-14 12:54 -0700
Re: Padding involved Tim Rentsch <txr@alumni.caltech.edu> - 2014-03-29 14:44 -0700
Re: Padding involved glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2014-03-29 03:50 +0000
Re: Padding involved James Kuyper <jameskuyper@verizon.net> - 2014-03-29 09:02 -0400
Re: Padding involved Stephen Sprunk <stephen@sprunk.org> - 2014-03-29 13:19 -0500
Re: Padding involved James Kuyper <jameskuyper@verizon.net> - 2014-03-28 21:21 -0400
Re: Padding involved Eric Sosman <esosman@comcast-dot-net.invalid> - 2014-03-28 15:27 -0400
Re: Padding involved Kaz Kylheku <kaz@kylheku.com> - 2014-03-28 19:54 +0000
Re: Padding involved Stephen Sprunk <stephen@sprunk.org> - 2014-03-28 15:02 -0500
Re: Padding involved Kaz Kylheku <kaz@kylheku.com> - 2014-03-08 00:43 +0000
Re: Padding involved Eric Sosman <esosman@comcast-dot-net.invalid> - 2014-03-07 20:20 -0500
Re: Padding involved anish singh <anish198519851985@gmail.com> - 2014-03-07 13:49 -0800
Re: Padding involved James Kuyper <jameskuyper@verizon.net> - 2014-03-07 16:46 -0500
Re: Padding involved "BartC" <bc@freeuk.com> - 2014-03-07 21:59 +0000
Re: Padding involved anish kumar <yesanishhere@gmail.com> - 2014-03-07 14:34 -0800
Re: Padding involved "BartC" <bc@freeuk.com> - 2014-03-07 23:59 +0000
Re: Padding involved Keith Thompson <kst-u@mib.org> - 2014-03-07 15:15 -0800
Re: Padding involved "BartC" <bc@freeuk.com> - 2014-03-08 10:08 +0000
Re: Padding involved Ben Bacarisse <ben.usenet@bsb.me.uk> - 2014-03-08 12:39 +0000
Re: Padding involved Keith Thompson <kst-u@mib.org> - 2014-03-08 14:03 -0800
Re: Padding involved Malcolm McLean <malcolm.mclean5@btinternet.com> - 2014-03-08 09:01 -0800
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