Can you call a C# DLL from a C DLL?

The most straight forward way of doing this is to expose one of the C# classes in your C# DLL as a COM object, and then create an instance of it from your C/C++ DLL. If that isn't an acceptable option, you'd need to create a mixed-mode C++ DLL (which contains both managed and unmanaged code). Your C/C++ DLL can call exported functions in your mixed-mode DLL, which can in turn forward the calls on to your C# class.

This article might help you out:

CLR Hosting APIs (MSDN)

Updated: There's a tool called mergebin that ships with the .NET SQLite wrapper you can use to create a mixed mode native/managed DLL. Grab the source code from:

SQLite for ADO.NET 2.0 (SourceForge)

You'll find the exe in the bin\tools folder.

Kev

It is actually pretty easy. Just use NuGet to add the "UnmanagedExports" package to your .Net project. See https://sites.google.com/site/robertgiesecke/Home/uploads/unmanagedexports for details.

You can then export directly, without having to do a COM layer. Here is the sample C# code:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Runtime.InteropServices;
using System.Text;
using System.Threading.Tasks;
using RGiesecke.DllExport;

class Test
{
    [DllExport("add", CallingConvention = CallingConvention.Cdecl)]
    public static int TestExport(int left, int right)
    {
        return left + right;
    }
}

R should be able to load TextExport just like a regular C dll.