[Ada (ObjectAda 7.2.2)] Creating VB6 DLLs

Creating DLLs for use by VB6 seems to be somewhat of a dark art. From what Roger Pearse, in his The Noddy Guide to using ADA code with Visual Basic says, it doesn't appear to be something easily achieved.

So far I've achieved it, to a certain extent, with ObjectAda and GNAT/GPL. The code for the ObjectAda implementation is below. I'll post the GNAT/GPL stuff in the next couple of days, God willing.

BO_DLib.adb, BO_D.adb and BO_D.ads are all based, albeit rather loosely, on sample files in winapi\samples\petzold\ch19\edrlib\

First up, BO_DLib.adb

-- ====================================================================================== -- -- -- -- Converted from Programming Windows 95 / Charles Petzold -- 4th ed. -- -- Chapter 19 EDRLIB.C: Easy Drawing Routine Library Module -- -- -- -- ====================================================================================== -- with BO_B; procedure BO_BLib is begin null; end BO_BLib;

Next, the spec file, BO_D.ads

There are six routines:

• procedure Bob1 calls dobox to show a messagebox.
• function Bob2 returns a long value, 1.
• function Bob3 receives a long and adds 21 to it.
• procedure Bob4 receives a long pointer to a string and passes it to dobox for display.
  I can pass Unicode to it and have it rendered appropriately.
• function Bob5 receives a long pointer to a string and returns a long being the length of the string.
• function Bob6 receives a long pointer to a string and catenates a string to it.
  "Danger, Will Robinson!" ... this is not how to do it and VB complains bitterly.

Okay, there are seven routines, but dobox isn't exported. It takes a pointer to a wide string and passes it to Win32.Winuser.MessageBoxW. I got dobox from a sample file as well.

-- ====================================================================================== -- -- -- -- Converted from Programming Windows 95 / Charles Petzold -- 4th ed. -- -- Chapter 19 EDRLIB.C: Easy Drawing Routine Library Module -- -- -- -- ====================================================================================== -- with Win32.Windef; package BO_B is procedure bob1; function Bob2 return Win32.LONG; function bob3 ( arg : Win32.LONG ) return Win32.LONG; procedure Bob4( Arg : win32.LPCWSTR ); function bob5( Arg : win32.PCWSTR ) return win32.LONG; procedure dobox (msg : Win32.PCWSTR); procedure Bob6( Arg : Win32.LPWSTR ); pragma Export (DLL_Stdcall, Bob1, "Bob1"); pragma export (DLL_Stdcall, Bob2, "Bob2"); pragma export (DLL_Stdcall, Bob3, "Bob3"); pragma Export (DLL_Stdcall, Bob4, "Bob4"); pragma Export (DLL_Stdcall, Bob5, "Bob5"); pragma Export (DLL_Stdcall, Bob6, "Bob6"); end BO_B;

And, finally, BO_D.adb, where the definitions given in BO_D are fleshed out.

-- ====================================================================================== -- -- -- -- Converted from Programming Windows 95 / Charles Petzold -- 4th ed. -- -- Chapter 19 EDRLIB.C: Easy Drawing Routine Library Module -- -- -- -- ====================================================================================== -- with Interfaces.C; with interfaces.C.Strings; use interfaces; with Ada.Unchecked_Conversion; with Interfaces.C.Strings; with System; with Win32.Crt.Direct; with Win32.Crt.Stdlib; with Win32.Winbase; with Win32.Windef; with Win32.Wingdi; with Win32.Winmain; with Win32.Utils; with Win32.Winuser; with win32; use win32; with Win32.windowsx; package body BO_B is procedure bob1 is msg : Win32.PCWSTR; HELLOMSG : constant WCHAR_Array := "Hello" & Wide_Nul; begin Msg := Addr(HELLOMSG); dobox(Msg); end bob1; function Bob2 return Win32.LONG is begin return 1; end bob2; function bob3 ( arg : Win32.LONG ) return Win32.LONG is use type Win32.LONG; sum : Win32.LONG; begin Sum := Arg + 21; return Sum; end Bob3; procedure Bob4( Arg : win32.PCWSTR ) is begin dobox(arg); end Bob4; function Bob5( Arg : win32.PCWSTR ) return win32.LONG is Arguments_Length : constant Win32.LONG := Win32.LONG (Win32.Winbase.lstrlenW (Arg)); begin return Arguments_Length; end Bob5; procedure Bob6( Arg : Win32.LPWSTR ) is H : Wide_String := Wide_String'("doo dah, doo dah"); c : Win32.lpwstr; begin c := win32.winbase.lstrcatW( Arg, Addr(H) ); end Bob6; procedure dobox (msg : Win32.PCWSTR) is IResult : Win32.INT; begin iResult := Win32.Winuser.MessageBoxW(System.Null_Address, Msg, Addr("Title"), 0); end dobox; end BO_B;

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

• I declared the functions and procedures as DLL_Stdcall in BO_D.ads so the routines come in decorated, thus the use of Alias in the Declare line. I used Microsoft's Dependency Walker to discover to what extent the names had been mangled.
• A reference to SCRRUN.DLL was added to the project, making possible the use of the FileSystemObject.
• Bob6 barges past the limit set for the string by VB, so things get a bit unstable. I'm still working through how to pass strings back.

Declare Sub Bob1 Lib "bo_blib.dll" Alias "_Bob1@0" () Declare Function Bob2 Lib "bo_blib.dll" Alias "_Bob2@0" () As Long Declare Function Bob3 Lib "bo_blib.dll" Alias "_Bob3@4" (ByVal i As Long) As Long Declare Sub Bob4 Lib "bo_blib.dll" Alias "_Bob4@4" (ByVal ptr As Long) Declare Function Bob5 Lib "bo_blib.dll" Alias "_Bob5@4" (ByVal ptr As Long) As Long Declare Sub Bob6 Lib "bo_blib.dll" Alias "_Bob6@4" (ByVal ptr As Long) Dim oFSO As New Scripting.FileSystemObject Dim oStream As Scripting.TextStream Sub main() Dim s As String Set oStream = oFSO.OpenTextFile("c:\temp\hua.txt", ForReading, False, TristateTrue) s = oStream.ReadLine oStream.Close Bob1 Debug.Print Bob2 Debug.Print Bob3(21) Bob4 (StrPtr(s)) Debug.Print Bob5(StrPtr(s)) Bob6 StrPtr(s) MsgBox s End Sub

By the way, if you think my code sucks, say so. I'm a total newb when it comes to Ada. Critiques are always welcome. King Solomon said, "The wise person accepts instructions." and also "Better is open rebuke than hidden love."

© Copyright Bruce M. Axtens., 2007