Re: Problem creating bindings - please help

["Steve" <nospam_steved94@comcast.net>]

"Gerd" <GerdM.O@t-online.de> wrote in message 
news:1147934783.645893.274580@u72g2000cwu.googlegroups.com...
> Hi all,
>
> I tried to create my own Ada bindings for a dll, but I didn't succeed.
>

I haven't done this with GNAT, but I have done similar work with ObjectAda. 
I have a few noted suggestions below.

>
> The C-header contains:
>
> DWORD __stdcall CAN_GetHwParam(
>        HCANHW hHw,
>        WORD   wParam,
>        void*  pBuff,
>        WORD   wBuffLen);
>
>
> My Ada-spec look like this:
>
> with System;

  with Interfaces;

>
> package CanApi2 is
>
> pragma Linker_Options ("-lCanApi2");
>
> subtype
>  HCANHW is Integer;
>

You need to look up the definition of HCANHW to find out the size.  I prefer 
to use either:

  Interfaces.Unsigned_16;
  Interfaces.Unsigned_32;
  Interfaces.Integer_16;
  Interfaces.Integer_32;

Since you are working with an interface.  Some people prefer to use types 
defined in Interfaces.C, I prefer to be more explicit for interfacing.

> subtype
>  Word is Integer;

Assuming you're working on Win32, this should be:

  subtype Word is Interfaces.Unsigned_16;

>
> function CAN_GetHwParam (hHw : HCANHW; wParam : Word; pBuff :
> System.Address; wBuffLen : Word) return Integer;
>
> private
>    pragma Import (Stdcall, CAN_GetHwParam, External_Name =>
> "CAN_GetHwParam");
> end CanApi2;
>
> The lib-file (CanApi2.lib) contains this names:
>
> _CAN_GetHwParam@16 __imp__CAN_GetHwParam@16 _CAN_SetHwParam@12
> __imp__CAN_SetHwParam@12
>
>
> And that's what I get when build my test-program:
>
> C:\Work\CAN>gnatmake cantest
> gcc -c cantest.adb
> gcc -c canapi2.ads
> gnatbind -x cantest.ali
> gnatlink cantest.ali
> ./cantest.o(.text+0x264):cantest.adb: undefined reference to
> `CAN_GetHwParam@16'
>
> gnatlink: cannot call C:\GNAT\bin\gcc.exe
> gnatmake: *** link failed.
>
> DLL2DEF shows this:
>
> EXPORTS
> CAN_GetHwParam
>
>
> So what's wrong with my code? Please help, thanks.
>
> Gerd
>

The other thing I have moved toward is loading the dll dynamically at run 
time.  If the dll is loaded automatically when the program runs, 
uncontrolled meaningless error messages (to an end user) appear and the 
program fails.  By loading dynamically I can put out a meaningful error 
message.  It is also easier to troubleshoot.

Here is an example of a few code fragments I use to set up a dynamic 
interface to adagraph.

   type PutpixelAccType is access
     function(X, Y, Hue : Integer) return Integer;
   pragma Convention( C, PutpixelAccType );

   PutpixelAcc : PutpixelAccType;

   function To_PutpixelAcc is
     new Ada.Unchecked_Conversion( WinDef.FarProc, PutpixelAccType );

   PutpixelProcName : C.Char_Array := C.To_C( "PutPixel" );

   procedure Put_Pixel (X, Y : in Integer; Hue : in Color_Type := White) is
      Return_Value : Integer;
   begin
      if PutPixelAcc /= null then
         Return_Value := PutPixelAcc(X, Y, Color_Type'Pos (Hue));
         if Return_Value < No_Errors then
            Make_Exception (Return_Value);
         end if;
      end if;
   end Put_Pixel;

-----------------------------------------------

   adagraphLibraryName : C.Char_Array := C.To_C( "adagraph.dll" );
begin
   adagraphDll := System.Null_Address;
   adagraphDll := WinBase.LoadLibrary( adagraphLibraryName(0)'access );
 ...
   PutpixelAcc := To_PutpixelAcc( WinBase.GetProcAddress( adagraphDll, 
PutpixelProcName(0)'access ) );
...

I hope this helps,

Steve
(The Duck)