Re: Enumeration representation clause surprise.

[richtmyer@cox.net]

On Jun 11, 7:38 am, Markus Schoepflin <nos...@no.spam> wrote:
> Hello,
>
> please consider the following code snippet:

etc

-----
Interesting. I had been playing with a similar example, and have
modified it a bit
to present. What got me is the record type with length 1 but an object
with that
type that was length zero! (It compiles without any warnings).

------------------------------ test1.2.ada
--------------------------------------
--
-- GPS 4.2.1 (20080115) hosted on pentium-mingw32msv
-- GNAT GPL 2007 (20070405-41)
--
--  X_Type'size     =  31
--  X_Rec_Type'size =  32
--  X_Rec'size      =  32
--  Y_Rec_Type'size =  1
--  Y_Rec'size      =  8
--  X_Rec.X1        =  2147483647
--  Y_Rec.X1        =  2147483647

--  GPS Pro 4.1.1 (20070423) hosted on i686-pc-linux-gnu
--  GNAT Pro 6.1.1 (20080111-41)
--
--  X_Type'size     =  31
--  X_Rec_Type'size =  32
--  X_Rec'size      =  32
--  Y_Rec_Type'size =  1
--  Y_Rec'size      =  0             -- this object is smaller than
its type!
--  X_Rec.X1        =  2147483647
--  Y_Rec.X1        =  2147483647

-------------------------------------------------------------------------

with ada.exceptions;  use ada.exceptions;
with interfaces.c;
with text_io;   use text_io;
with unchecked_conversion;

procedure test1 is

   type X_Type is ( X );
   for x_type use (x => 16#7FFF_FFFF#);

   type X_Rec_Type is
      Record
        X1 : X_Type;
      End Record;

   X_Rec : X_Rec_Type := (X1 => x);

   type Y_Rec_Type is
      Record
        X1 : X_Type;
      End Record;
   for Y_Rec_Type'size use 0;

   for Y_Rec_Type use
      Record
        X1 at 0 range 0 .. -1;                   -- Minus 1  !!
      End Record;

   Y_Rec : Y_Rec_Type := (X1 => X);

   function convert is new unchecked_conversion (X_type, natural);
begin

   put_line("X_Type'size     = " & X_Type'size'img);
   put_line("X_Rec_Type'size = " & X_Rec_Type'size'img);
   put_line("X_Rec'size      = " & X_Rec'size'img);
   put_line("Y_Rec_Type'size = " & Y_Rec_Type'size'img);
   put_line("Y_Rec'size      = " & Y_Rec'size'img);
   put_line("X_Rec.X1        = " & convert(X_Rec.X1)'img);
   put_line("Y_Rec.X1        = " & convert(Y_Rec.X1)'img);

end test1;