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Re: How does strict aliasing work with parallel arrays in a union or const-initialized data

From Bartc <bc@freeuk.com>
Newsgroups comp.lang.c
Subject Re: How does strict aliasing work with parallel arrays in a union or const-initialized data
Date 2015-10-29 10:55 +0000
Organization A noiseless patient Spider
Message-ID <n0stru$plq$1@dont-email.me> (permalink)
References (4 earlier) <b49266e4-9532-4179-9d4c-fd2c02d7236b@googlegroups.com> <lnlhambmrj.fsf@kst-u.example.com> <kfnoafibkpk.fsf@x-alumni2.alumni.caltech.edu> <lnh9labhuv.fsf@kst-u.example.com> <342e8770-35cb-4f9c-ad01-8a660c12d97d@googlegroups.com>

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On 29/10/2015 03:02, supercat@casperkitty.com wrote:

> I wish C would honor its history as a systems-programming language and let
> programmers excercise control over struct layouts.

I think you can.

You can use something like #pragma pack(1). Then it will use byte 
alignment for all fields, and it is up to you to space things out by 
selecting member sizes and inserting padding.

But the explicit padding will add extra fields which will affect things 
like initialisation.

(Outside of I've always used byte alignment, which means carefully 
crafting a struct layout if I care about alignment or overall size. When 
converting one byte-aligned language to high-level C, then it simplest 
to turn on #pragma pack(1) and let C lay things out my way, than to try 
and predict what C will do.)

-- 
Bartc

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Thread

How does strict aliasing work with parallel arrays in a union or const-initialized data supercat@casperkitty.com - 2015-10-21 16:47 -0700
  Re: How does strict aliasing work with parallel arrays in a union or const-initialized data Tim Rentsch <txr@alumni.caltech.edu> - 2015-10-24 21:20 -0700
    Re: How does strict aliasing work with parallel arrays in a union or const-initialized data supercat@casperkitty.com - 2015-10-25 11:44 -0700
      Re: How does strict aliasing work with parallel arrays in a union or const-initialized data Tim Rentsch <txr@alumni.caltech.edu> - 2015-10-28 12:15 -0700
        Re: How does strict aliasing work with parallel arrays in a union or const-initialized data supercat@casperkitty.com - 2015-10-28 14:25 -0700
          Re: How does strict aliasing work with parallel arrays in a union or const-initialized data Keith Thompson <kst-u@mib.org> - 2015-10-28 16:23 -0700
            Re: How does strict aliasing work with parallel arrays in a union or const-initialized data Tim Rentsch <txr@alumni.caltech.edu> - 2015-10-28 17:08 -0700
              Re: How does strict aliasing work with parallel arrays in a union or const-initialized data Keith Thompson <kst-u@mib.org> - 2015-10-28 18:09 -0700
                Re: How does strict aliasing work with parallel arrays in a union or const-initialized data supercat@casperkitty.com - 2015-10-28 20:02 -0700
                Re: How does strict aliasing work with parallel arrays in a union or const-initialized data Bartc <bc@freeuk.com> - 2015-10-29 10:55 +0000
                Re: How does strict aliasing work with parallel arrays in a union or const-initialized data supercat@casperkitty.com - 2015-10-29 06:50 -0700
                Re: How does strict aliasing work with parallel arrays in a union or const-initialized data Keith Thompson <kst-u@mib.org> - 2015-10-29 08:52 -0700
                Re: How does strict aliasing work with parallel arrays in a union or const-initialized data supercat@casperkitty.com - 2015-10-31 10:21 -0700
                Re: How does strict aliasing work with parallel arrays in a union or const-initialized data Keith Thompson <kst-u@mib.org> - 2015-10-29 08:50 -0700
                Re: How does strict aliasing work with parallel arrays in a union or const-initialized data supercat@casperkitty.com - 2015-10-29 12:25 -0700
                Re: How does strict aliasing work with parallel arrays in a union or const-initialized data Tim Rentsch <txr@alumni.caltech.edu> - 2015-10-30 13:02 -0700
                Re: How does strict aliasing work with parallel arrays in a union or const-initialized data Keith Thompson <kst-u@mib.org> - 2015-10-30 13:35 -0700
                Re: How does strict aliasing work with parallel arrays in a union or const-initialized data Tim Rentsch <txr@alumni.caltech.edu> - 2015-10-30 19:57 -0700
                Re: How does strict aliasing work with parallel arrays in a union or const-initialized data Keith Thompson <kst-u@mib.org> - 2015-10-31 12:27 -0700
                Re: How does strict aliasing work with parallel arrays in a union or const-initialized data Eric Sosman <esosman@comcast-dot-net.invalid> - 2015-10-30 17:02 -0400
                Re: How does strict aliasing work with parallel arrays in a union or const-initialized data Keith Thompson <kst-u@mib.org> - 2015-10-30 14:16 -0700
                Re: How does strict aliasing work with parallel arrays in a union or const-initialized data supercat@casperkitty.com - 2015-10-31 08:13 -0700
                Re: How does strict aliasing work with parallel arrays in a union or const-initialized data Tim Rentsch <txr@alumni.caltech.edu> - 2015-10-31 08:42 -0700
                Re: How does strict aliasing work with parallel arrays in a union or const-initialized data supercat@casperkitty.com - 2015-10-31 10:40 -0700
                Re: How does strict aliasing work with parallel arrays in a union or const-initialized data Tim Rentsch <txr@alumni.caltech.edu> - 2015-11-02 01:45 -0800
                Re: How does strict aliasing work with parallel arrays in a union or const-initialized data supercat@casperkitty.com - 2015-11-02 06:57 -0800
                Re: How does strict aliasing work with parallel arrays in a union or const-initialized data Tim Rentsch <txr@alumni.caltech.edu> - 2015-11-02 08:12 -0800
                Re: How does strict aliasing work with parallel arrays in a union or const-initialized data supercat@casperkitty.com - 2015-11-02 08:54 -0800
                Re: How does strict aliasing work with parallel arrays in a union or const-initialized data Tim Rentsch <txr@alumni.caltech.edu> - 2015-11-04 07:24 -0800
                Re: How does strict aliasing work with parallel arrays in a union or const-initialized data supercat@casperkitty.com - 2015-11-04 09:22 -0800
                Re: How does strict aliasing work with parallel arrays in a union or const-initialized data Tim Rentsch <txr@alumni.caltech.edu> - 2015-11-04 19:48 -0800
                Re: How does strict aliasing work with parallel arrays in a union or const-initialized data supercat@casperkitty.com - 2015-11-05 09:44 -0800
                Re: How does strict aliasing work with parallel arrays in a union or const-initialized data Tim Rentsch <txr@alumni.caltech.edu> - 2015-11-07 10:17 -0800
                Re: How does strict aliasing work with parallel arrays in a union or const-initialized data raltbos@xs4all.nl (Richard Bos) - 2015-11-10 15:37 +0000
                Re: How does strict aliasing work with parallel arrays in a union or const-initialized data supercat@casperkitty.com - 2015-11-10 09:01 -0800
          Re: How does strict aliasing work with parallel arrays in a union or const-initialized data Tim Rentsch <txr@alumni.caltech.edu> - 2015-10-28 16:48 -0700
        Re: How does strict aliasing work with parallel arrays in a union or const-initialized data Keith Thompson <kst-u@mib.org> - 2015-10-28 16:11 -0700
          Re: How does strict aliasing work with parallel arrays in a union or const-initialized data Tim Rentsch <txr@alumni.caltech.edu> - 2015-10-28 16:37 -0700

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