Access methods from ATL dll file in C#

I've been working with trying to link up some c++ code and wrap it inside a COM object to access via C#. I created an atl project and added a simple method such as Add(double a, double b). The following is the code from my atl.h file:

// atl.h : Declaration of the Catl
#pragma once
#include "resource.h"       // main symbols

#include "com_i.h"


#if defined(_WIN32_WCE) && !defined(_CE_DCOM) && !defined(_CE_ALLOW_SINGLE_THREADED_OBJECTS_IN_MTA)
#error "Single-threaded COM objects are not properly supported on Windows CE platform, such as the Windows Mobile platforms that do not include full DCOM support. Define _CE_ALLOW_SINGLE_THREADED_OBJECTS_IN_MTA to force ATL to support creating single-thread COM object's and allow use of it's single-threaded COM object implementations. The threading model in your rgs file was set to 'Free' as that is the only threading model supported in non DCOM Windows CE platforms."
#endif



// Catl

class ATL_NO_VTABLE Catl :
public CComObjectRootEx<CComSingleThreadModel>,
public CComCoClass<Catl, &CLSID_atl>,
public Iatl
{
public:
Catl()
{
}

DECLARE_REGISTRY_RESOURCEID(IDR_ATL)

DECLARE_NOT_AGGREGATABLE(Catl)

BEGIN_COM_MAP(Catl)
COM_INTERFACE_ENTRY(Iatl)
END_COM_MAP()



DECLARE_PROTECT_FINAL_CONSTRUCT()

HRESULT FinalConstruct()
{
    return S_OK;
}

void FinalRelease()
{
}

public:

STDMETHOD(Add)(DOUBLE a, DOUBLE b);
};

OBJECT_ENTRY_AUTO(__uuidof(atl), Catl)

The following is from the atl.cpp file

// atl.cpp : Implementation of Catl

#include "stdafx.h"
#include "atl.h"

STDMETHODIMP Catl::Add(DOUBLE a, DOUBLE b)
{
// TODO: Add your implementation code here

return a + b;
}

Inside my c# file I'm calling the dll... after i referenced it... it sees the dll but not the methods assigned. which is my problem. Heres the code from program.cs

sing System.Collections.Generic;
using Syste开发者_运维知识库m.Linq;
using System.Text;
using System.Runtime.InteropServices;

namespace sharpdll
{
class Program
{
    [DllImport("com.dll")]
    public static extern double Add(double a, double b);

    static void Main(string[] args)
    {
        Add(2, 3);
    }
}
}

Debugging breaks at Add(2, 3); Says "Unable to find an entry point named 'Add' in DLL 'com.dll'." Any ideas?

DllImport is for PInvoke (to native Win32 dlls).
You want COM Interop.

Register your ATL com object, then Add a reference to it, as you would to any .Net or COM component.

An alternative to ATL, you can expose your C++ functionality through C++/CLI.

Hope this helps,