Calling C# .NET Service From C++ Application?

Question

I have an old MFC app written in Visual Studio 6. This will at some point be rewritten in C# .NET. However, before then I have to write a couple of new Windows services for the existing application. The others were written in ATL. What I would prefer to do is write these new services in C# .NET so that when the rest of the application is rewritten, these don't need to be.

Is it going to be possible to call the interfaces on the libraries hosted in a .NET windows service from the old application? If so, could you please explain how.

Answer 1

Absolutely. You're looking for a feature of .NET called COM-Interop.

http://msdn.microsoft.com/en-us/library/kew41ycz%28v=vs.71%29.aspx

http://msdn.microsoft.com/en-us/magazine/cc163494.aspx

The second link has an ATL example.

EDIT: Based on your feedback in the comments, let me expand on this...

Ah - you're right about the sample on that page.

The first link is really where you want to start for all the details. If you follow the links, you'll find this page:

"Exposing .NET Framework Components to COM" http://msdn.microsoft.com/en-us/library/zsfww439%28v=vs.71%29.aspx

Essentially, it's just a matter of applying a series of attributes to your classes and properties, and then generating the appropriate registry entries on the client machine (which .NET has a tool to do - see: http://msdn.microsoft.com/en-us/library/bctyca52%28v=vs.71%29.aspx)

I've done this several times myself for .NET projects people needed to call from VC++ and/or VB6.

Some other links that might be of interest:

http://www.codeproject.com/KB/COM/nettocom.aspx <-- Perfect example of what you're trying to do.

http://www.codeproject.com/KB/COM/Universal_CCW.aspx

Answer 2

I've done this exact thing with an MFC-based C++ application in Visual Studio 2008 and a .NET-based C# Windows service.

First, if you have not created the C# Windows services yet, I've got a couple of tutorials for creating the basic framework. The first tutorial provides a step-by-step procedure for creating the service and writing events to an application-specific event log. The second tutorial shows how to modify the service to install and uninstall itself from the command line, which I find of great use.

Second, you need to decide how you are going to communicate between your MFC application and your Windows service. Any kind of inter-process communication (IPC) model will work - sockets, pipes, shared memory, WCF, etc. Since you are wanting to migrate to .NET anyway, I would recommend using Windows Communication Foundation (WCF), which is the way I've done it. Specifically, I chose the named pipe aspect of WCF for my communication method based on the chart shown here.

If you go down the WCF route, you'll benefit from the fact that the communication between application and service is .NET-based. Thus, when you move your application to .NET, the communication mechanism won't have to be rewritten. The trick in the meantime is getting your MFC application to use the WCF code. To do this, write the WCF client code in a .NET assembly using C#. Then, use a C++ dll to bridge the gap between your MFC code and the .NET assembly. I've got another tutorial with step-by-step instructions for how to do this.

Hope this helps.