Calling .NET dll from native C++

Question

I have a problem calling a .NET dll (mclNET.dll) using my COM wrapper. This is a third part dll which I do not have source code of. Basically I want to use this mclNET.dll in my pure native C++ application, so I am developing a C# wrapper. MCLWrapper.dll, that makes the methods in mclNET.dll visible. Here is what I did:

• In MCLWrapper.dll, I added the mclNET.dll as reference, then define the interface to make the mclNET.dll methods visible. here is some of my code:

  using System;            
  using System.Collections.Generic;            
  using System.Linq;            
  using System.Text;           
  using mclNET;       
  
  namespace MCLWrapper       
  {            
       public interface MCLControl            
       {                
            void MCLConnect(string SerialNumber);                
            void MCLSet_Switch(string SwitchName, int Val);                
            void MCLDisconnect();         
       };
  
       public class MCLControlClass:MCLControl
       {
           private USB_RF_SwitchBox _sb = new USB_RF_SwitchBox();
  
           public void MCLConnect(string SerialNumber)
           {            
               _sb.Connect(ref SerialNumber);
           }
  
           public void MCLSet_Switch(string SwitchName, int Val)
           {
               _sb.Set_Switch(ref SwitchName, ref Val);
           }
  
           public void MCLDisconnect()
           {
               _sb.Disconnect();
           }
       }
   }
  

And this is the AssemblyInfor.cs for MCLWrapper.dll:

using System.Reflection;
using System.Runtime.CompilerServices;
using System.Runtime.InteropServices;

// General Information about an assembly is controlled through the following 
// set of attributes. Change these attribute values to modify the information
// associated with an assembly.
[assembly: AssemblyTitle("MCLWrapper")]
[assembly: AssemblyDescription("")]
[assembly: AssemblyConfiguration("")]
[assembly: AssemblyCompany("")]
[assembly: AssemblyProduct("MCLWrapper")]
[assembly: AssemblyCopyright("Copyright ©  2013")]
[assembly: AssemblyTrademark("")]
[assembly: AssemblyCulture("")]
//[assembly: AssemblyKeyFile("..\\MCLWrapper.SNK")]


// Setting ComVisible to false makes the types in this assembly not visible 
// to COM components.  If you need to access a type in this assembly from 
// COM, set the ComVisible attribute to true on that type.
[assembly: ComVisible(true)]

// The following GUID is for the ID of the typelib if this project is exposed to COM
[assembly: Guid("14fa8796-ee52-4e39-8481-f893ad92bb68")]

// Version information for an assembly consists of the following four values:
//
//      Major Version
//      Minor Version 
//      Build Number
//      Revision
//
// You can specify all the values or you can default the Build and Revision Numbers 
// by using the '*' as shown below:
// [assembly: AssemblyVersion("1.0.*")]
[assembly: AssemblyVersion("1.0.0.0")]
[assembly: AssemblyFileVersion("1.0.0.0")]

• Then after I built this Wrapper.dll, I registered the it using regasm command, to generate a .tlb file

• Then in my native C++ application, I imported the tlb file, and tried to use the Wrapper.dll which referred the NET.dll. Here is some code in native C++ application:

  #include "stdafx.h"
  #include "math.h"
  #include "DetectorSwitch.h"
  #include "DetectorSwitchSetupXML.h"
  #include "OleAuto.h"
  
  #import "C:/MyPath/MCLWrapper.tlb" raw_interfaces_only   
  
  wchar_t message[256];
  using namespace MCLWrapper;
  
  long DetectorSwitch::FindDevices(long &deviceCount)
  {
      long ret = TRUE;
  
      deviceCount=0;
  
         HRESULT hCoInitialize = CoInitialize(NULL);
  
      MCLControlPtr MySwitch(__uuidof(MCLControlClass));
  
      HRESULT hConnet = MySwitch->MCLConnect(_SN);    // connect to sc
  
      short output  = 1;
      MySwitch->MCLSet_Switch(&_A,&output);
  
  }
  

Now the problem is, it does not recognize MySwitch->MCLSet_Switch(&_A,&output) function, which means, the mclNET.dll is not fully exposed to my native C++ code yet.

I am wondering what is the problem here? How I can by any chance correct it? How exactly can I call a .NET dll in my native C++ application? Many thanks up front.

Cushing

Have you tried to add a ComVisible attribute on the interface and class? – Naevus

I think I have a COM visible attribute set as true in AssemblyInfo.cs. Let me paste it then you can see if it is what you are referring to. – Cushing

Is it possible that you got the parameters on MCLSet_Switch wrong? &output looks like the address of a short but the function seems to want an int. – Schwarzwald

The problem is, when I typed MySwitch->, it did not automatically show MCLSet_Switch(); And when I complied MCLWrapper, it said MCLSet_Switch() not recognized. – Cushing

Ok it's good at assembly level. Maybe the namespace to use in C++ is not MCLWrapper, check the beginning of the .TLH file that has been created in the Debug or Release configuration directory by the #import directive. – Naevus

Hi ALl: I solved the problem. I think I basically did two things: 1. Download there latest dll; 2. Create a project and clean pasted my old code. Somehow I got it work. – Cushing

You can now decompile .NET DLLs with DotPeek. – Lindo

Answer 1

I solved the problem finally. I think I basically did two things:

1. Download there latest NET.dll;

2. I created a new project "MCLWrapper" which generates a new MCLWrapper.dll and clean pasted the code from my old project.

Maybe there is something I messed up in my old project that I did not realize. Maybe it was the new NET.dll did the magic. I have no idea. I basically repeated what I have done, but this time pretty cleanly.

Somehow I got it work. So basically, my original thread is pretty much how to call a .NET dll from native C++ code. Hope my experience will be helpful for you.

Cushing

Answer 2

#import <mscorlib.tlb> raw_interfaces_only
#import C:/MyPath/MCLWrapper.tlb" no_namespace named_guids

Try is above mentioned import statements - works for me and call your .net code without any namespaces from your native C++.

Laboy

Sorry, I think you are right, but I just got my problem fixed somehow. But I will keep your tips in mind. Thanks. – Cushing