Question

I want to write an algorithmic library in standard, platform-independent C++.

Can I then take the same C++ code and compile it for .NET so that a C# application can use the library?
If not, what is the easiest way to achieve this kind of interop?

Answer 1

You have three ways to expose your library to easily be called from managed code:

• write a C++/CLI wrapper for it that contains a public ref class – the C# code will call methods of this class, which will call native methods of your library
• expose a C-style function from your library as a DLL – the C# code will use P/Invoke to call the function
• write a COM component in C++ that uses your library and call it from the C# code by adding a COM reference to it.

That third one, COM, I include only for completeness. It wouldn’t be my first choice. Or my third. It’s one thing if the COM component exists, it’s another to write it just for this.

Between the first two it’s a matter of who else might use this library. If the C# code is the only one using it, do what you like. But for example you might have 15 or 20 native methods that set various properties, followed by a go or execute method that does the actual work. Because managed-native interop has a cost, I would tell you to write one C++/CLI function that takes 20 parameters, calls the various native functions and then calls the go or execute. This gives you a chunkier interface instead of chatty and reduces your interop costs.