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

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4.82 (28 votes)
13 Dec 2013CPOL
Describes with an example of how you can call C#.NET methods from unmanaged C++ code.


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;
                value = 2;

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)

__declspec(dllexport) void ShowMessageBox(int *value)
    ManagedDll::DoWork work;    

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;


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


    return 0;

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


This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)


About the Author

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Comments and Discussions

QuestionWorks perfectly with C++-Application but not with C-DLL Pin
Member 1105861225-Jul-19 19:54
memberMember 1105861225-Jul-19 19:54 
Questionyou are mistaking a very basic of C/C++ Pin
Member 116277472-Aug-18 20:04
memberMember 116277472-Aug-18 20:04 
Questionthanks Pin
Member 1252329021-May-18 5:34
memberMember 1252329021-May-18 5:34 
QuestionThe missing steps not in the original posting Pin
Wendel Renner28-Aug-17 4:52
memberWendel Renner28-Aug-17 4:52 
QuestionNeed consultant to accomplish calling C# function from C++ Pin
Wendel Renner25-Aug-17 4:27
memberWendel Renner25-Aug-17 4:27 
QuestionBuilds ok but... can't build in my application Pin
stevecodeproject24-Aug-16 4:40
memberstevecodeproject24-Aug-16 4:40 
AnswerRe: Builds ok but... can't build in my application Pin
rabbit only26-May-17 1:27
memberrabbit only26-May-17 1:27 
QuestionHow to pass a String and int Pin
wang200230-Jan-16 14:58
memberwang200230-Jan-16 14:58 
AnswerRe: How to pass a String and int Pin
MiCRo_5-Dec-17 7:46
memberMiCRo_5-Dec-17 7:46 
AnswerRe: How to pass a String and int Pin
Member 1252329021-May-18 5:33
memberMember 1252329021-May-18 5:33 
GeneralMy vote of 5 Pin
Aqua_Aria23-Nov-15 18:20
memberAqua_Aria23-Nov-15 18:20 
QuestionError Pin
Member 1177530818-Jun-15 5:26
memberMember 1177530818-Jun-15 5:26 
AnswerRe: Error Pin
Greg Mulvihill20-Sep-15 4:19
memberGreg Mulvihill20-Sep-15 4:19 
AnswerRe: Error Pin
Michael Waters3-Jan-19 11:34
memberMichael Waters3-Jan-19 11:34 
I had the same problem. You need to set up the configuration options in the Linker to look for ManagedDll.lib. Just copy "ManagedDll.lib" into field Linker->Input->Additional Dependencies in the configuration options property page for TestApp. It's already there for Release builds. Toggle back and forth between the builds and look for the differences, and you'll find it.

Question__declspec(dllexport) cannot be applied to a function with the __clrcall calling convention Pin
Sai Gopinath Dokku18-May-15 17:41
memberSai Gopinath Dokku18-May-15 17:41 
AnswerRe: __declspec(dllexport) cannot be applied to a function with the __clrcall calling convention Pin
MiCRo_5-Dec-17 6:35
memberMiCRo_5-Dec-17 6:35 
SuggestionNice! Pin
Shawn-USA6-May-15 18:07
memberShawn-USA6-May-15 18:07 
Question64 bit? Pin
KodeMnke26-Apr-15 6:12
memberKodeMnke26-Apr-15 6:12 
Questionuseful Solution Pin
Member 1163486823-Apr-15 23:23
memberMember 1163486823-Apr-15 23:23 
GeneralMy vote of 1 Pin
Sergey Alexandrovich Kryukov19-Mar-15 14:03
memberSergey Alexandrovich Kryukov19-Mar-15 14:03 
GeneralRe: My vote of 1 Pin
BigTimber@home23-Dec-15 3:50
professionalBigTimber@home23-Dec-15 3:50 
GeneralRe: My vote of 1 Pin
Sergey Alexandrovich Kryukov23-Dec-15 5:30
memberSergey Alexandrovich Kryukov23-Dec-15 5:30 
GeneralRe: My vote of 1 Pin
Member 1209768521-Dec-16 6:00
memberMember 1209768521-Dec-16 6:00 
GeneralRe: My vote of 1 Pin
Sergey Alexandrovich Kryukov21-Dec-16 17:23
memberSergey Alexandrovich Kryukov21-Dec-16 17:23 
GeneralRe: My vote of 1 Pin
David Thielen24-Mar-17 11:48
memberDavid Thielen24-Mar-17 11:48 

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Posted 11 Dec 2013


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