Call unmanaged C++ VS 6.0 MFC dll from C#

Question

I have an unmanaged C++ MFC dll that was developed in VS 6.0. I would like to use it in my C# app. I'm trying to use PInvoke.

Here is the C++ code:

// testDll.cpp : Defines the entry point for the DLL application.
//
#include "stdafx.h"


extern "C" {

BOOL APIENTRY DllMain( HANDLE hModule, 
                       DWORD  ul_reason_for_call, 
                       LPVOID lpReserved
                     )
{
    return TRUE;
}

 __declspec(dllexport) int test(int a)
{
    return a * a;
}
}

And here is how I'm trying to invoke the method "test" from C#:

// PInvokeTest.cs
using System;
using System.Runtime.InteropServices;

class PlatformInvokeTest
{

    [DllImport("TestDll.dll")]
    internal static extern int test(int number);

    public static void Main()
    {
        Console.WriteLine(test(5));     
    }
}

This approach works just fine when I set C++ dll to be just a regular Win32 dll.

But once I change the project type to MFC ("Use MFC in a Shared DLL") I'm getting this error:

Unhandled Exception: System.DllNotFoundException: Unable to load DLL 'TestDll.dll': The specified module could not be found. (Exception from HRESULT: 0x8007007E) at PlatformInvokeTest.test(Int32 number)

Thanks!

Hassan Syed Hassan Syed · Accepted Answer · 2009-12-16T20:05:41

The DLL needs to be in a path where the system can pick it up. have you put it in the directory where your application starts ? (probably in a DEBUG folder of you VS solution).

The second option is to give it the absolute path of the DLL.

The third option is to place it in "c:\windows\System" but this is a '-1' approach :D

Call unmanaged C++ VS 6.0 MFC dll from C#

3 Answers