Calling DLL created with Aonix Object Ada from Visual Basic

[steve.woodward@uk.thalesgroup.com (Steve Woodward)]

I have some Ada code that needs to be run from a MS Access front end.
The plan is to link the Ada code as a DLL, then call the DLL from VB
code in Access.

Parameter passing is proving difficult.  I have got integers to work
(both directions) but not booleans, strings or arrays of integers. 
From previous articles I learned that I should be using the parameter
passing convention DLL_Stdcall.

This is the Ada for for a function that returns the sum of two
integers:

   function DLLSumOf (X: Integer; Y: Integer) return integer;
   pragma Export(DLL_Stdcall,DLLSumOf,"DLLSumOf");
   -- next line is required according to
www.tertullian.org/rpearse/ada_dll.htm
   pragma Suppress (All_checks, on => DLLSumOf);

I used the MS utilty "Dependency Walker" to look inside the DLL I
created, and found it had the function name "_DLLSumOf@8".  So this is
the Alias name that I put into the VB declaration, as follows:

Private Declare Function DLLSumOf Lib
"H:\Ada\tryitout\AddThem\AddThem-Win32(Intel)-Debug\dll.dll" _
Alias "_DLLSumOf@8" (ByVal X As Integer, ByVal Y As Integer) As
Integer

This works! Now using the same technique I tried a function that does
nothing more than return a boolean set to false.  VB puts the returned
value in a check box.

Ada:
function ReturnFalse return boolean;
   pragma Export(DLL_Stdcall, ReturnFalse,"ReturnFalse");
   pragma Suppress (All_checks, on => ReturnFalse);  
 
VB:
Private Declare Function ReturnFalse Lib
"H:\Ada\tryitout\AddThem\AddThem-Win32(Intel)-Debug\dll.dll" _
Alias "_ReturnFalse@0" () As Boolean

When I run this, the check box becomes "true", not "false" as
expected.  When I tried to pass a boolean IN to a function, the result
implied that the DLL saw it as "true" even when the VB had set it to
"false".

Can anybody spot what I am doing wrong?
How do I pass strings?
How do I pass arrays of integers??
Is it possible to pass user-defined types which include arrays???

Steve Woodward