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From: jerry@jvdsys.nextjk.stuyts.nl (Jerry van Dijk)
Subject: Re: ada routine reading c data problem
Date: 1997/04/05
Message-ID: <860206044.12snx@jvdsys.nextjk.stuyts.nl>#1/1
X-Deja-AN: 230757472
Distribution: world
References: <33441A45.454D@ny.essd.northgrum.com>
Organization: *JerryWare HQ*, Haarlem, Holland
Newsgroups: comp.lang.ada
Date: 1997-04-05T00:00:00+00:00
List-Id: <comp.lang.ada>


>I am running on a WINNT pc using gnat.  I have a program that has both
>ada and c modules.  I need to be able to access the c structures from
>the ada code.  Is there any way of doing this besides a special c
>routine to send back the data.

Yes, if the structures are accesible according to C rules you can define
the struct in Ada and import the actual instantiations. In GNAT this
couldn't be simpler:

   /* c.c */
   #include <stdio.h>

   struct a_struct {
      int a;
      float b;
   } var_a;

   void display_struct(void)
   {
      printf("Struct values are: a -> %d, b -> %f\n", var_a.a, var_a.b);
   }

   -- test.adb
   procedure Test is

      type A_Struct is
         record
            A : Integer;
            B : Float;
         end record;

      Var_A : A_Struct;
      pragma Import (C, Var_A);

      procedure Display_Struct;
      pragma Import (C, Display_Struct);

   begin
      Var_A.a := 1;
      Var_A.b := 2.0;
      Display_Struct;
   end Test;

to test:

   gcc -c c.c
   gcc -c test.adb
   gnatbind -x test.ali
   gnatlink test.ali c.o

Note that depending on the struct you might have to pack items or the stuct,
in using it as an argument, you might run into copy by reference vs copy by
value issues. See the GNAT user manual for more details.

--

-- Jerry van Dijk       | Haarlem, Holland
-- Business Consultant  | Team Ada
-- Ordina Finance       | jdijk@acm.org