Re: Interfacing with C

["Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>]

On Mon, 18 May 2009 04:29:44 -0700 (PDT), cedric wrote:

> I would like to connect a C interface to another software package with
> my Ada programs.
> 
> The h-file of the api contains the following pre-processor commands:
> 
> #ifdef SPSSXD_EXPORTS
> # define SPSSXD_API __declspec(dllexport)
> #else
> # if MS_WINDOWS
> #   define SPSSXD_API __declspec(dllimport)
> # else
> #   define SPSSXD_API
> # endif
> #endif

From this you should figure out the call convention. It can be either C or
stdcall. The rest can be usually ignored. Usually this stuff tells whether
the entry point is a reference or else a vector for dynamic run-time
linking or else an entry point, when the library itself is compiled,
nothing interesting for an Ada client.

> Some functions headers are
> 
> SPSSXD_API bool IsBackendReady();
> SPSSXD_API int SetUpFromSPSS(SpssAdapter* anAdapter, SpssXDSmb*
> anSmb);
> 
> What do I have to do to get a connection between the C functions and
> my Ada program with regard to the commands of the pre-processor?

Print the preprocessor output if you are in doubts. Otherwise it could be
like this:

   with Interfaces.C;  use Interfaces.C;
   ...
   function IsBackendReady return Int; -- C does not have Boolean
   pragma Import (stdcall, IsBackendReady, "IsBackendReady");

   type SpssAdapter is record
       ... -- Components of struct SpssAdapter
   end record;
   pragma Convention (C, SpssAdapter);

   type anSmb is record
       ... -- Components of struct anSmb
   end record;
   pragma Convention (C, anSmb);

   function SetUpFromSPSS
      (  anAdapter : access SpssAdapter;
          anSmb : access SpssXDSmb
      );
   pragma Import (stdcall, SetUpFromSPSS, "SetUpFromSPSS");

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de