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From: Simon Wright <simon@pushface.org>
Newsgroups: comp.lang.ada
Subject: Re: Interfacing between Ada and C: records and structs
Date: Tue, 31 Jul 2012 20:23:45 +0100
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Date: 2012-07-31T20:23:45+01:00
List-Id: <comp.lang.ada>

awdorrin <awdorrin@gmail.com> writes:

> private
>   type Dummy is tagged null record;
>   type Mutex is record
>     Mutex : aliased POSIX.C.pthread_mutex_t;
>     D : Dummy;
>   end record

What's D : Dummy doing here? There's no equivalent in the C.

Here, on an x86_64 compiler,

   package Mutex is
      type pthread_mutex_t is new Boolean with
        Alignment => 8,
        Size => 192;
      type Dummy is tagged null record;
      type Mutex is record
         Mutex : aliased pthread_mutex_t;
         D : Dummy;
      end record;
   end Mutex;

compiled with -gnat12 -gnatR3 gives

   for Pthread_Mutex_T'Size use 192;
   for Pthread_Mutex_T'Alignment use 8;

   for Dummy'Size use 64;
   for Dummy'Alignment use 8;
   for Dummy use record
      _Tag at 0 range  0 .. 63;
   end record;

   for Mutex'Size use 256;
   for Mutex'Alignment use 8;
   for Mutex use record
      Mutex at  0 range  0 .. 191;
      D     at 24 range  0 .. 63;
   end record;