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From: tmoran@bix.com
Subject: Re: Binding a type to a union.
Date: 1999/11/24
Message-ID: <rRM_3.686$Tc2.68834@typhoon-sf.snfc21.pbi.net>#1/1
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References: <383b8e49@rsl2.rslnet.net>
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X-Trace: typhoon-sf.snfc21.pbi.net 943430103 206.170.2.186 (Tue,
 23 Nov 1999 23:55:03 PST)
Organization: SBC Internet Services
NNTP-Posting-Date: Tue, 23 Nov 1999 23:55:03 PST
Newsgroups: comp.lang.ada
Date: 1999-11-24T00:00:00+00:00
List-Id: <comp.lang.ada>

>Its use may be a little worrying if you have portability issues to consider,
Often you have just one, or very few, objects of the schizophrenic type,
in which case you might prefer:

with ada.text_io;
with interfaces.c,
     system.address_to_access_conversions;
procedure foobar is
use interfaces;

type foo_struct is
   record
      x : C.Int;
   end record;
for foo_struct use record
  x at 0 range 0 .. 31;
end record;
for foo_struct'size use 32;

type some_enum_type is (a,b);

type bar_struct is
   record
      x : C.char;
      y : some_enum_type;
   end record;
for bar_struct use record
  x at 0 range 0 .. 7;
  y at 1 range 0 .. 7;
end record;
for bar_struct'size use 32;

package foo_locs is new system.address_to_access_conversions(foo_struct);

--Then you can make a foo and a bar at the same place in memory.
-- (See Cohen, 2nd Edition, section 19.3 for some warnings)

foo : aliased foo_struct;
foo_loc : constant system.address := foo_locs.to_address(foo'access);
bar : bar_struct;
for bar'address use foo_loc;

begin

  foo.x := 3;
  bar.y := b;

  ada.text_io.put_line(c.int'image(foo.x));

end foobar;