[ Late reply, but this may help others ]

Well, I think that should not be too difficult. You can use DllImport.

Say you have the following C++ func in a dll :
Code: c++
// int Sum (int, int) inside MyDll.dll
int Sum(int x, int y)
{      return x + y;      }
and you want to use it in your C# app.

So, you can use it like this :
Code: c#
using System;
using System.Collections.Generic;
using System.Text;
using System.Runtime.InteropServices; //For "DllImport"

namespace MyCSharp
      class Program
      [DllImport("MathFuncsDll.dll", CharSet = CharSet.Auto)]
      public static extern Int32 Sum(Int32 a, Int32 b);

            static void Main()
                  Console.WriteLine(Sum(3, 4));

Simple, isn't it ?

PS : Just embed a manifest to avoid the error : "An application has made an attempt to load the C Runtime library without using a manifest."