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From: Stephen Leake <Stephen.Leake@gsfc.nasa.gov>
Subject: Re: Help with access-to-functions and imported C functions
Date: 1997/08/20
Message-ID: <33FB4226.384E@gsfc.nasa.gov>#1/1
X-Deja-AN: 265532573
References: <33F31D5B.71B2@mail.connect.usq.edu.au>
Reply-To: Stephen.Leake@gsfc.nasa.gov
Organization: NASA Goddard Space Flight Center -- Greenbelt, Maryland USA
Newsgroups: comp.lang.ada
Date: 1997-08-20T00:00:00+00:00
List-Id: <comp.lang.ada>


Matthew Kennedy wrote:
> 
> ...
> 
> It seems how ever, that I cannot assign the access of an imported C
> function (please see code below for the exact error message) to an
> access variable of the same 'type' of function.
>
> ...
>    Random := Random_Gaussian'Access;   -- gives compile error
> "subprogram has invalid convention for context"
> 

As this message is (somewhat cryptically) trying to tell you, you have
specified different calling conventions for Random and Random_Gaussian.
You need to use "pragma Convention". Note that you must apply the pragma
to both the access type, and the function "Two":

with Ada.Text_IO, Interfaces.C;
use  Ada.Text_IO, Interfaces.C;
procedure Test
is
   package Double_IO is new Ada.Text_IO.Float_IO(Double);
   use Double_IO;

   type Function_Access is access function return Double;
   pragma Convention (C, Function_Access);

   function Random_Gaussian return Double; -- double
RandomGaussian(void);
   function Random_Uniform return Double;  -- double
RandomUniform(void);

   pragma Import(C, Random_Gaussian, "RandomGaussian");
   pragma Import(C, Random_Uniform, "RandomUniform");

   function Two return Double;
   pragma Convention (C, Two);

   function Two return Double is
   begin
      return 2.0;
   end Two;

   Random : Function_Access;
   Y : Double;

begin
   Random := Two'Access;
   Random := Random_Gaussian'Access;
   Y := Random.all;
   Put(Y);
   New_Line;
end Test;

> --
> Matthew Kennedy
> Student of Electronics Engineering
> University of Southern Queensland, Australia
>   "When will you realise your already there?"
>       - Marilyn Manson

-- 
- Stephe