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Newsgroups: comp.lang.ada
Subject: Re: combine Ada with MS VS C++
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From: Ludovic Brenta <ludovic.brenta@insalien.org>
Date: Wed, 16 Mar 2005 22:44:42 +0100
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Date: 2005-03-16T22:44:33+01:00
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 writes:
> Thanks,How would you declared this in ada an MS VS C++ for a procedure
> the procedures is as follows in Ada. Vr and Vl are two global double
> variablers in the C++ program.
>
> Ada:
>
> procedure CheckBuffer(vr,vl : in out is Interfaces.C.double);
>
> Do I need to write something special in the *.DEF file?? except from
> EXPORTS CheckBuffer

I don't program on Windows, so I can't help you with the exporting
from Ada.  You may need to use all three arguments to pragma Export in
order to get the link name right; this is the platform-dependent part.
So you'd say something like:

procedure Check_Buffer (vr, vl : in out Interfaces.C.double);
pragma Export (Convention => C, Entity => Check_Buffer,
               External_Name => "CheckBuffer", -- this is...
               Link_Name => "something");      -- ...the hard part

Once you've done this, you would import this procedure into C++ as
follows:

extern "C" void CheckBuffer (double* vr, double* vl);

The "C" is necessary to avoid C++ name mangling by the linker.

Per Ada Reference Manual, B.3(68):

      68. (...) an Ada out or in out parameter
          of an elementary type T, is passed as a t* argument to a C
          function, where t is the C type corresponding to the Ada type
          T. In the case of an elementary out or in out parameter, a
          pointer to a temporary copy is used to preserve by-copy
          semantics.

-- 
Ludovic Brenta.