[Ada (GNAT/GPL)] Creating DLLs for VB6

As promised, the GNAT/GPL code. Based on Roger Pearse's The Noddy Guide to using ADA code with Visual Basic.

How I ended up with the names api.ads, api.adb and api.def is an artefact from something I was reading. [This space set aside for an attribution.]

First up, api.ads, which declares the functions and exports them.

• function Factorial, which accepts a C.int and returns a C.int
• procedure Mangle, which accepts a Win32.LPWSTR and attempts the same dangerous stuff that Bob6 does in the ObjectAda version. Still working on this one.
• function Pattern, which returns a Win32.LPWSTR
• procedures Initialize_API, and Finalize_API, which I understand are mandatory. (If someone knows better, please tell me.)

with Interfaces.C; use Interfaces; with Win32; use Win32; package API is Count : C.int := 0; function Factorial (Val : C.int) return C.int; procedure Mangle( Ptr : Win32.LPWSTR ); function Pattern return Win32.LPWSTR; procedure Initialize_API; procedure Finalize_API; -- Initialization & Finalization routines. More in the next section. private pragma Export (DLL, Initialize_API); pragma Export (DLL, Finalize_API); --pragma Export (StdCall, Count); pragma Export (DLL, Factorial ); pragma Export (DLL, Mangle ); pragma Export (DLL, Pattern ); end API;

Next, api.adb, where the declarations are explained.

Mangle replaces the incoming string with something of its own. If the incoming string is larger or the same size then everything's more or less okay. (Less in the latter case, but at least it doesn't crash.) However, if the incoming string is shorter, VB truncates up to the length it knows about, and who knows what damage we've done with whatever gets overwritten by the rest of foo.

Pattern returns a pointer to the string data. Not knowing a lot about Ada, I don't know if the contents of foo will still be there by the time VB looks it and reads out.

with Interfaces.C; use Interfaces.C; with Win32; use Win32; with Win32.Winmain; with Win32.Winbase; with System; package body API is function Factorial (Val : C.int) return C.int is Fact : C.int := 1; begin Count := Count + 1; for K in 1 .. Val loop Fact := Fact * K; end loop; return Fact; end Factorial; procedure Mangle( Ptr : Win32.LPWSTR ) is lp : Win32.lpwstr; foo : Wide_String := Wide_String'("foo man chew"); begin lp := Win32.Winbase.lstrcpyW( Ptr, Win32.Addr(foo) ); end Mangle; function Pattern return Win32.LPWSTR is foo : Wide_String := Wide_String'("foo man chew"); begin return Win32.Addr(foo); end Pattern; procedure Initialize_API is procedure Adainit; pragma Import (C, Adainit); begin Adainit; end Initialize_API; procedure Finalize_API is procedure Adafinal; pragma Import (C, Adafinal); begin Adafinal; end Finalize_API; end API;

api.def lists the symbols exported, and is needed by gnatdll.

EXPORTS factorial mangle initialize_api finalize_api pattern

Now, pulling it all together requires some handwaving on the commandline.

gnat make api -Ic:\gnat\2007\include\win32ada gnatdll -e api.def -d api.dll api.ali -Ic:\gnat\2007\lib\win32ada

The output from a run of these is as follows:

C:\Docume...ts\BO_DLL>gnat make api -Ic:\gnat\2007\include\win32ada gcc -c -Ic:\gnat\2007\include\win32ada api.adb gcc -c -I.\ -Ic:\gnat\2007\include\win32ada -I- c:\gnat\2007\include\win32ada\win32.adb gcc -c -I.\ -Ic:\gnat\2007\include\win32ada -I- c:\gnat\2007\include\win32ada\win32-winbase.adb gcc -c -I.\ -Ic:\gnat\2007\include\win32ada -I- c:\gnat\2007\include\win32ada\win32-winmain.adb gcc -c -I.\ -Ic:\gnat\2007\include\win32ada -I- c:\gnat\2007\include\win32ada\stdarg.adb gcc -c -I.\ -Ic:\gnat\2007\include\win32ada -I- c:\gnat\2007\include\win32ada\stdarg-impl.adb gcc -c -I.\ -Ic:\gnat\2007\include\win32ada -I- c:\gnat\2007\include\win32ada\win32-utils.adb gcc -c -I.\ -Ic:\gnat\2007\include\win32ada -I- c:\gnat\2007\include\win32ada\win32-windef.adb gcc -c -I.\ -Ic:\gnat\2007\include\win32ada -I- c:\gnat\2007\include\win32ada\win32-winnt.adb gcc -c -I.\ -Ic:\gnat\2007\include\win32ada -I- c:\gnat\2007\include\win32ada\stdarg-machine.ads C:\Documen...ts\BO_DLL>gnatdll -e api.def -d api.dll api.ali -Ic:\gnat\2007\lib\win32ada Building relocatable DLL... make api.dll and libapi.a Warning: resolving _finalize_api by linking to _finalize_api@0 Use --enable-stdcall-fixup to disable these warnings Use --disable-stdcall-fixup to disable these fixups Warning: resolving _initialize_api by linking to _initialize_api@0 Warning: resolving _mangle by linking to _mangle@4 Warning: resolving _pattern by linking to _pattern@0 Warning: resolving _factorial by linking to _factorial@4 Warning: resolving _finalize_api by linking to _finalize_api@0 Use --enable-stdcall-fixup to disable these warnings Use --disable-stdcall-fixup to disable these fixups Warning: resolving _initialize_api by linking to _initialize_api@0 Warning: resolving _mangle by linking to _mangle@4 Warning: resolving _pattern by linking to _pattern@0 Warning: resolving _factorial by linking to _factorial@4

Now the VB code. Take note of a few things:

• Exporting as DLL generates decorated names, but gnatdll was able to resolve the decorated ones with the undecorated ones specified in api.def
• For reasons I remember reading somewhere, initialize_api and finalize_api are mandatory, and must be the first and last calls to the DLL
• Seeing as woof woof woof woof is longer than foo man chew, s ends up containing foo man chew
  woof

Declare Sub initialize_api Lib "api.dll" () Declare Function factorial Lib "api.dll" (ByVal x As Integer) As Integer Declare Function pattern Lib "api.dll" () As Long Declare Sub mangle Lib "api.dll" (ByVal x As Long) Declare Sub finalize_api Lib "api.dll" () Sub main() Dim s As String s = "woof woof woof woof" initialize_api Debug.Print factorial(3) mangle StrPtr(s) Debug.Print Len(s), s finalize_api End Sub

Next stop is to get this working with "GNAT/GCC MS-Windows MinGW 4.2.1 R0". I would prefer to be working under the GMGPL.

© Copyright Bruce M. Axtens., 2007