Message-ID:	<3F04C1B6.9E036018@somewhere.nil>
Date:	Fri, 04 Jul 2003 01:52:22 +0200
From:	Gautier Write-only <gautier AT somewhere DOT nil>
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Newsgroups:	comp.os.msdos.djgpp
Subject:	Re: data alignment issue
References:	<00A224F4 DOT 86EC817C DOT 6 AT st DOT fmph DOT uniba DOT sk>
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To:	djgpp AT delorie DOT com
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Viktor DOT Stujber AT st DOT fmph DOT uniba DOT sk:

> I've noticed that djgpp aligns all members of a structure to 4 bytes.

Not necessarily (see below).

> ---------------------------------------------------------------------
> | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 |
> ----------------------------------------------------
> | a   _   _   _   b   b   b   b   c    c    _    _ |
> ----------------------------------------------------
> 
> this is the layout of this structure in memory:
> struct {
>  BYTE a;
>  DWORD b;
>  WORD c;
> }

with Interfaces;                use Interfaces;
with Ada.Integer_Text_IO;       use Ada.Integer_Text_IO;

procedure Align is

  type r1 is record
    a: Unsigned_8;  -- 1
    b: Unsigned_32; -- 4
    c: Unsigned_16; -- 2
  end record;

  type r2 is record
    a: Unsigned_8;  -- 1
    b: Unsigned_32; -- 4
    c: Unsigned_16; -- 2
  end record;
  pragma pack(r2);

begin
  Put(r1'size/8); Put(r2'size/8);
end;

DJGPP takes 10 bytes for r1 (choice) and 7 for r2 (it must,
because of "pack").
________________________________________________________
Gautier  --  http://www.mysunrise.ch/users/gdm/gsoft.htm

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