Calling C# .NET methods from unmanaged C/C++ code

• Download C_To_Managed_Call.zip - 45.2 KB

Introduction

For a number of reasons which I won't get into, I needed to use a C# .NET DLL from unmanaged code. I spent a long time looking for the answer before figuring it out. So I thought I'd post the example here to spread the word.

The way it works is fairly straightforward and requires three components:

1. C# DLL doing whatever.
2. Managed C++ DLL with exposed C function. This DLL will call your C# DLL methods. 
3. Unmanaged C++ application/DLL which will call the exposed C function in the Managed C++ DLL.

Using the code

Create your C# DLL. The below example just shows a simple MessageBox and sets the result of the value based on OK or CANCEL.

// ManagedClass.cs

// Any source code blocks look like this
//

using System;
using System.Collections.Generic;
using System.Text;
using System.Windows.Forms;
using System.IO;

namespace ManagedCSharp
{
    public static class ManagedClass
    {
        public static void ShowValue(ref int value)
        {
            DialogResult result = MessageBox.Show("C# Message Box", 
                    "C# Message Box", MessageBoxButtons.OKCancel);

            if (result == DialogResult.OK)
                value = 1;
            else
                value = 2;
            return;
        }
    }
}

Create a Managed C++ DLL and reference it in your C# project.

This exports your function ShowMessageBox in an unmanaged format.

Inside the exported function, call the Managed C++ method which calls your C# methods.

// ManagedDll.h

#pragma once

using namespace System;
using namespace System::Reflection;

namespace ManagedDll {    

    public ref class DoWork
    {
        public:void ShowCSharpMessageBox(int *value)
        {            
            ManagedCSharp::ManagedClass::ShowValue(*value);
            return;
        }
    };
}

__declspec(dllexport) void ShowMessageBox(int *value)
{
    ManagedDll::DoWork work;    
    work.ShowCSharpMessageBox(value);    
}

Create your unmanaged C or C++ DLL or EXE and call the exposed C++ method in your managed code.

In your unmanaged project setting, you will need to reference the ManagedDll.lib file created by the ManagedDll project and build time.

// TestApp.cpp : Defines the entry point for the console application.
//

#include "stdafx.h"
#include "conio.h"
#include <iostream>
#include <windows.h>

_declspec(dllexport) void ShowMessageBox(int *value);


int _tmain()
{
    int *result;

    ShowMessageBox(result);

    if(*result == 1)
        printf("Ok Was Pressed \n");
    else
        if(*result == 2)
            printf("Cancel Was Pressed \n");
        else
            printf("Unknown result \n");

    system("pause");

    return 0;
}

Find the attached full project which should build straight away. Built in Visual Studio 2008.