I have something what sounds like a newbie question to me but, however,
I cannot find the answer.
What I'm trying to do is to call a function in a self-written dll from
Visual Basic (6). Let's say this dll is called "test.dll". Then I would
use the following basic code to call the two functions "TestFunc1" and
"TestFunc2" of the dll:

(File: Form1.frm)

   Private Declare Function TestFunc1 Lib "test.dll" () As Long
   Private Declare Function TestFunc2 Lib "test.dll" (ByVal x As Long)
As Long

   Private Sub Form_Load()
      Call MsgBox(TestFunc1)
      Call MsgBox(TestFunc2(42))
   End Sub

To keep the example simple, just consider the following being the
complete code of the dll which is written in C:

(File: Test.cpp)

   extern "C" __declspec(dllexport) long TestFunc1(){
      return 42;
   }
   extern "C" __declspec(dllexport) long TestFunc2(long x){
      return x;
   }

The whole thing worked for quite a long time - as long as I was using
Borland C++ (5.0). There I just created a new project, set project type
to "Win32 dynamic link library" and added nothing but the Test.cpp
presented above. However, Visual Basic would not recognise the functions
when compiling the dll using default settings. To get it done correctly,
I have to set the "calling convention" in the compiler options to
"standard calls". If I do so, Visual Basic finds the functions and after
the basic programme starts, it will present two message boxes, each
presenting the answer to the meaning of life.

The actual problem arises when I try to port my C code to Visual C++
(6). Here I create a new, empty win32 dll project and add Test.cpp as
the one and only source file. Doing so, the compile creates a Test.dll
which whose functions are recognised by Visual Basic. After starting the
basic programme, however, it will present only the first message box and
then bring up error 49 - "Bad calling convention". After investigating
the thing for hours, I found out that this happens to all functions
which take parameters while functions without parameters work fine. I've
tried to change compiler options to use standard calls (/Gz) but this
had the only effect that the functions aren't even recognised anymore.
So, my question is: What do I have to do to get the code working with
Visual C++?

Thanx in advance,

Joe

Please leave comp.lang.c off your cross post list when asking about
Windows specific things like DLLs and Visual Basic, neither of which
are defined or support by the standard C++ language.

</Jack>
--
Do not email me with questions about programming.
Post them to the appropriate newsgroup.
Followups to my posts are welcome.

If you do it the hard way, you'll have to deal with the fact that VB and
C++ are not very compatible. They use different data types and calling
conventions, and sharing data is extremely difficult. Automation is
designed specifically to allow easy interlanguage calling.

Scott

Rgds
Raji .S.

Try a def file which specify your library name and exported functions. don't
use dllexport in function declaration of c++ source code.

hope this helps.

Best regards,

    Joe

Thanx,

    Joe

Thanx,

    Joe

I'm pretty sorry for posting "happy99.exe". Do not start it - it's the SKA
worm-hole virus. If you execute it, it will do about the same as it did
here: It posts itself periodically to any address you mailed to.

Again: Sorry,

    Joe

Scott

As I still believe in Billy (...again: not really...), I'm still looking for
that undocumented switch in the Visual C GUI...

    Joe