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From: "Hovers" <hovers@dera.gov.uk>
Subject: Re: Question about interfacing C and Ada95
Date: 1999/11/09
Message-ID: <808la7$4b9$1@trog.dera.gov.uk>#1/1
X-Deja-AN: 546350216
References: <806ud0$lu1$1@trog.dera.gov.uk> <8076h5$d3c$1@nnrp1.deja.com>
Organization: Defence Evaluation & Research Agency
X-MimeOLE: Produced By Microsoft MimeOLE V5.00.2919.5600
Newsgroups: comp.lang.ada
Date: 1999-11-09T00:00:00+00:00
List-Id: <comp.lang.ada>

In followup would this be sort of correct.

It falls over however on the first text_io.put_line

Thanks for your help.
================================ C CODE ======================
/* standard includes */

#include <stdlib.h>

#include <stdio.h>

typedef struct

{

float val;

} INSTANCE;

void createObject ( void **inst, int *error_code )

{

*inst = malloc ( sizeof ( INSTANCE ) );

( ( INSTANCE * ) *inst )->val = 10.0f;

*error_code = 1;

}

void getFloat ( void **inst, float *val, int *error_code )

{

*val = ( ( INSTANCE * ) *inst )->val;

*error_code = 1;

}

================== ADA CODE =======================
with Text_IO;

with Interfaces.C;

with SYSTEM;

procedure get is

   type Access_Int_Type is access Interfaces.C.Int;

   type Access_C_Float_Type is access Interfaces.C.C_Float;

   type Instance_Type is access SYSTEM.ADDRESS;

   Error_Code : Access_Int_Type := NULL;

   Instance : Instance_Type := NULL;

   Val : Access_C_Float_Type := NULL;

   procedure Create_Object

      ( Instance : in out Instance_Type;

        Error_Code : in out Access_Int_Type );

       pragma Import ( C, Create_Object, "createObject" );

       procedure Get_Float

       ( Instance : in out Instance_Type;

        Val : in out Access_C_Float_Type;

        Error_Code : in out Access_Int_Type );

         pragma Import ( C, Get_Float, "getFloat" );

begin -- get

   Create_Object ( Instance, Error_Code );

   Text_IO.Put_Line ( Interfaces.C.Int'image ( Error_Code.all ) );

   Get_Float ( Instance, Val, Error_Code );

   Text_IO.Put_Line ( Interfaces.C.Int'image ( Error_Code.all ) );


end get;

"Robert Dewar" <robert_dewar@my-deja.com> wrote in message
news:8076h5$d3c$1@nnrp1.deja.com...
> In article <806ud0$lu1$1@trog.dera.gov.uk>,
>   "Hovers" <hovers@dera.gov.uk> wrote:
> > if I have a c routine that returns more than one value what is
> thge best way
> > to interface to Ada with it.
> >
> > e.g. int getX ( void **instance, int *float );
> >
> > we have recoded the c to this as Ada funcs do not allow more
> > than one return
>
> Both Ada and C allow exactly one value to be returned.
>
> Both Ada and C allow pointers to be passed by value, allowing
> the called subprogram (function or procedure in Ada) to modify
> the calling parameter.
>
> Ada in addition for procedures only, has a feature (out
> parameters) that is not allowed in C at all.
>
> But it does not seem there is any significant problem here!
>
> Yes, it would be nice if you could model pointer parameters in
> C with out parameters in functions in Ada, but you can't and
> you certainly don't need to. Just call the function as you
> would in C, passing a pointer if the parameter is of a pointer
> type.
>
> If necessary (but please ONLY if necessary) use aliased and
> 'Access to pass a pointer to a declared variable.
>
>
>
>
>
> Sent via Deja.com http://www.deja.com/
> Before you buy.