Using DLL import/Declare in VB.NET with parameter types not used by .NET

Question

I am working on a project where I have to import a DLL file into a VB project that was created a few years back. The DLL was created in C++, and looks like:

void CoordinateConversionService::convert( SourceOrTarget::Enum sourceDirection, SourceOrTarget::Enum targetDirection, CoordinateTuple* sourceCoordinates, Accuracy* sourceAccuracy, CoordinateTuple& targetCoordinates, Accuracy& targetAccuracy )

I am an intern at my job, and I haven't had to use this yet, so my understanding is extremely limited, along with my usage of VB (I'm a C++/C# guy). Here are a few questions:

1) Looking at Dllimport, it seems like the last part outside of the parameters is a return type. Example code from another site:

<DllImport("advapi32.dll")> _
  Public Function GetUserName( _
     ByVal lpBuffer As StringBuilder, _
     ByRef nSize As Integer) As Boolean

Is "As Boolean" the return type? If so, I tried using "Sub" and it says "Keyword does not name a type." Hence why I looked into declare, because it seems I CAN return void/sub as a return type.

2) Trying to use the types "CoordinateTuple" and "Accuracy" give me problems, saying that they aren't defined. How do I get around this since I don't think I can really define them, and what about the fact that they're pointers? Also - I cannot modify the C++ code in any way, so what I have is what I have.

Answer 1

In VB you say either Public Function Whatever (params) As ReturnType (which is the same as public ReturnType Whatever(params) in C#) or Public Sub Whatever (params) which is for things that don't return anything (return void in C++/C#).

If your function/sub takes custom types you will need to declare .NET equivalents to those as well. This can make PInvoke hard work. Tools like the interop assistant can help.

Answer 2

For the custom types, you may have to create a wrapper in managed C++, which has the ability both to consume native C++ APIs and expose managed APIs. Although dated, a walkthrough can be found here:

• Writing Managed Wrappers with Managed C++