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Groups > comp.lang.c > #59533

Re: Alignment requirement of basic types

From Keith Thompson <kst-u@mib.org>
Newsgroups comp.lang.c
Subject Re: Alignment requirement of basic types
Date 2015-04-03 10:50 -0700
Organization None to speak of
Message-ID <878ue9yucv.fsf@kst-u.example.com> (permalink)
References <mfm5mg$4rp$1@dont-email.me> <551EB3B9.7090206@verizon.net> <slrnmhtj1m.gus.usenet@xargs-spam.com>

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John Temples <usenet@xargs-spam.com> writes:
> On 2015-04-03, James Kuyper <jameskuyper@verizon.net> wrote:
>> C2011 requires that alignments must be powers of 2, no such requirement
>> existed in earlier versions of the C standard. I've no idea whether
>> there's ever been an implementation of C where that wasn't the case.
>
> I have used 8-bit platforms with C compilers that supported 24-bit
> integer and floating point types.  These platforms had no alignment
> requirements for multi-byte objects, so it was possible to have
> objects aligned on a three-byte boundary.

Sure, but the alignment of the type would be 1 byte, not 3.

A 32-bit int object on a system where int has a 4-byte alignment
requirement might *happen* to be aligned on, say, a 12-byte boundary,
but that's not meaningful.  The question on which James has no idea
(and neither do I) is whether any C implementation imposes a required
alignment that's not a power of 2.

-- 
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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Thread

Alignment requirement of basic types Noob <root@127.0.0.1> - 2015-04-03 15:48 +0200
  Re: Alignment requirement of basic types Tim Prince <tprince@computer.org> - 2015-04-03 10:23 -0400
  Re: Alignment requirement of basic types James Kuyper <jameskuyper@verizon.net> - 2015-04-03 11:37 -0400
    Re: Alignment requirement of basic types John Temples <usenet@xargs-spam.com> - 2015-04-03 17:21 +0000
      Re: Alignment requirement of basic types James Kuyper <jameskuyper@verizon.net> - 2015-04-03 13:45 -0400
        Re: Alignment requirement of basic types Kaz Kylheku <kaz@kylheku.com> - 2015-04-03 18:40 +0000
      Re: Alignment requirement of basic types Keith Thompson <kst-u@mib.org> - 2015-04-03 10:50 -0700
      Re: Alignment requirement of basic types glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-04-03 19:02 +0000
    Re: Alignment requirement of basic types Kaz Kylheku <kaz@kylheku.com> - 2015-04-03 18:01 +0000
  Re: Alignment requirement of basic types Richard Damon <Richard@Damon-Family.org> - 2015-04-03 12:05 -0400
    Re: Alignment requirement of basic types glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-04-03 16:48 +0000
  Re: Alignment requirement of basic types Kaz Kylheku <kaz@kylheku.com> - 2015-04-03 16:46 +0000
    Re: Alignment requirement of basic types Keith Thompson <kst-u@mib.org> - 2015-04-03 11:06 -0700
      Re: Alignment requirement of basic types Robert Wessel <robertwessel2@yahoo.com> - 2015-04-05 22:22 -0500
  Re: Alignment requirement of basic types Waldek Hebisch <hebisch@antispam.uni.wroc.pl> - 2015-04-04 23:15 +0000

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