How to create a wrapper DLL/Type Library in VB6?

Question

In my previous question, I asked why I kept getting the error message bad DLL calling convention when trying to call functions from a DLL. The general consensus was that I needed to change the calling convention to cdecl. Makes sense.

Unfortunately, I cannot place it right there on the function declaration importation. I had to either "create a wrapper DLL" or "create a type library for the DLL."

I am very unfamiliar with VB as my main focus at work is C# and this is the first time working in the language for a very long time. I'm not sure exactly how to accomplish this task.

I'm also confused as to how a wrapper DLL helps things. Supposedly I can't decorate a function import with cdecl in my code but if I move that exact function import to a new VB6 DLL and then reference that DLL it suddenly works?

Answer 1

I actually think this question was better on the topic.

To sum up, you can "place it right there on the function declaration importation", but the VB6 IDE doesn't know how to debug such a thing. But the compiler deals with it just fine. Once you compile it into a dll then your main project can access the functionality that was compiled.

Perhaps you are asking how to move these into a dll? If that is the case, you need to create a new Project of type "ActiveX Dll". Name it something like PwrUSB. Next, add a class (or rename the default/empty one if it is provided) to something like PwrUSBApi. Next, in the properties window, set the class to GlobalMultiUse. In a module called MDeclares, drop in all of your declarations:

'from your other post...
Public Declare Function InitPowerDevice CDecl Lib "PwrDeviceDll.dll" (ByRef firmware() As Byte) As Long

Back in your PwrUSBApi class:

'forward your calls to the dll
Public Function InitPowerDevice (ByRef firmware() As Byte) As Long
   InitPowerDevice  = MDeclares.InitPowerDevice(firmware)
End Function

You could create a more fully fledged object model from the API, but I'd start with this simple wrapper until you sort out all of the APIs.

Oh yeah, back in your main project you'd add a reference your new wrapper PwrUSB.dll in the Project menu. Then in the code you would use it something like this:

Dim numOfDevices as Long 
Dim firmware() As Byte
Redim firmware(0 to 31)
numOfDevices = PwrUSB.InitPowerDevice(firmware)

Good luck.

Answer 2

A wrapper DLL in VB6 would still need to use the CDecl decorator or else a typelib created to deal with the DLL's function signatures.

The only advantage in creating a VB6 wrapper for this is to make it easier to debug the calling program from within the VB6 IDE, where CDecl has no effect. The wrapper would be small, and created once as a native code DLL, making CDecl effective there.

See your other thread(s) for additional answers. I suspect your real problem is that you were not passing the right kind of argument.