Importing a class from a c# dll into a c++ app

Question

I need to import a dll made in c# from c++ All the examples I found import a single function from a dll, but as far as I know, you cannot export a single function from c# without exporting the whole class (I'm a bit of a c# newbie though)

I am using node gyp to compile it (I'm building a node module for my web app using v8)

Here is my c# code:

using System;
using System.IO;
using System.Runtime.InteropServices;

[ComVisible(true)]
public class Hello 
{
    public static void Main() 
    {
        Console.WriteLine("Hello World!");
        string createText = "Hello World" + Environment.NewLine;
        File.WriteAllText(".\\asd.txt", createText);
    }
}

And this is my c++ header file:

#ifndef ASDLIB_H
#define ASDLIB_H
#define ASD_IMPORT __declspec(dllimport)
#define STDCALL __stdcall

class ASD_IMPORT Hello{
    public:
         STDCALL static void ASD_IMPORT Main();
};

#endif // ASDLIB_H

Answer 1

I normally do this kind of stuff by creating a static C++ CLR Wrapper Lib.

These are the steps I'm normally using (although I don't use it very often):

Here minimal example with using Visual Studio:

1. Create managed C# .NET library Project

Let name it HelloLibManaged with one file Hello.cs and following content:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace HelloLibManaged
{
    public class Hello
    {
        public void Print()
        {
            System.Console.WriteLine("Hello from Managed Lib");
        }
    }
}

Build this lib with x86 or x64 , just dont Any CPU

2. Create a new C++ CLR static lib project within same solution. Let's name it HelloLibCpp

• Add a reference to HelloLibManaged project via Project->Add Reference

• Remove automatic created existing .h/.cpp files from Project, and create these 2 files:

HelloUnmanaged.h

#pragma once

namespace hello_managed {

    class Hello
    {
    public:
        void Print();
    };
}

and

HelloUnmanaged.cpp:

#include "HelloUnmanaged.h"

namespace hello_managed
{

    void Hello::Print()
    {
        HelloLibManaged::Hello^ hello = gcnew HelloLibManaged::Hello();
        hello->Print();
    }

}

Und Project Properties -> General specify static lib. In the Build settings specify x86 / x64 - use the same build type as building Managed lib from Step 1.

Now you can build the dll and use it in your other unmanaged C++ projects.

For more advanced stuff, like return types and methods with parameters you have to do Type-Marshalling between managed/unmanaged code. There are many resources online with more information about Type-Conversion between managed/unmanaged code. Keyword: Marshaling.