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From: Tom_Hargraves@Raytheon.com
Subject: Re: Binding a type to a union.
Date: 1999/11/23
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Thanks for the example of pragma Unchecked_Union in your reply. I have learnt
another pragma today :-)

However, wouldn't its use be restricted to when the type was to be used in a
'C' language interface call?

The pragma comes with a long list of restrictions which perhaps, generally,
would be undesirable.

Yours curiously,
Tom H.



"David Botton" <David@Botton.com> on 11/22/99 07:55:33 PM


Please respond to comp.lang.ada@ada.eu.org

From:"David Botton" <David@Botton.com> on 11/22/99 07:55 PM



To:  comp.lang.ada@ada.eu.org
cc:  (bcc: Tom Hargraves/RMD/Raytheon/CA)

Subject:  Re: Binding a type to a union.







You would do the following:

type foo_struct is
   record
      x : C.Int;
   end record;

type bar_struct is
   record
      x : C.char;
      y : some_enum_type;
   end record;

subtype Union_1_Range is Positive range 1..2;

type Union_1 (Which : Union_1_Range) is
   record
      case Which is
         when 1 =>
            foo : foo_struct;
         when 2 =>
            bar : bar_struct;
   end record;
pragma Unchecked_Union(Union_1);

type foo_type is
   record
     foo_bar : Union_1;
    end record;


Then you can access using:

my : foo_type;

my.foo_bar.foo.x := 1;

etc.

David Botton


Aidan Skinner wrote in message ...
>Can anybody tell me the correct way to give an Ada representation of a
>C union contained in a structure?
>
>Eg given a declaration in C of:
>
>struct foo
> {
>
>   union
>   {
>     struct
>     {
>       int x;
>     } foo
>
>     struct
>     {
>       char x;
>       some_enum_type y;
>     } bar
>
>   } foo_bar
> }
>
>What's the correct way of doing this given that x needs to be
>public?
>
>- Aidan




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