Re: Calling DLL created with Aonix Object Ada from Visual Basic

[Larry Hazel <lhhazel@otelco.net>]

Steve Woodward wrote:
> 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

Could there be a difference (size or bit pattern) between the VB and Ada 
representation of true and false?

Larry