dllexport in C#

BillL — Wed, 03 Jun 2009 15:17:00 GMT

Because C# does not provide a dllexport equivalent, you'll need to add a CPP shim into the mix that can get an instance of the managed class from the CLR. Here's the quick walkthrough:

1. Add a cpp library to the VSTA integration solution

2. Reference the VSTA Integration assembly from the cpp library project

3. Define a dllexport

4. Implement the dllexport

5. LoadLibrary on the cppdll

6. GetProcAddress of the exported func

7. Create a typedeclaration for the exported func signature

8. Call it

Here is the unmanaged CPP app code:

typedef void *(__stdcall _CreateInstance)(void);

typedef _CreateInstance *RTCCREATEINSTANCEPROC;

static RTCCREATEINSTANCEPROC lpfnRtcCreateInstance = NULL;

HMODULE hm = LoadLibrary(OLESTR("CppClassLibrary1.dll"));

if (hm != N ULL)

{

lpfnRtcCreateInstance = (RTCCREATEINSTANCEPROC)GetProcAddress(hm, "CreateInstance");

void *managedinterface = (*lpfnRtcCreateInstance)();

FreeLibrary(hm);

}

Here's the C# code:

using System;

using System.Collections.Generic;

using System.Text;

using System.Runtime.InteropServices;

namespace ClassLibrary1

{

[ComVisible(true)]

public interface Interface1

{

string HelloWorld { get; }

}

[ComVisible(true)]

public class Class1 : Interface1

{

#region Interface1 Members

public string HelloWorld

{

get

{

return "Hello World!";

}

#endregion

public static IntPtr CreateInstance()

{

return Marshal.GetComInterfaceForObject(new Class1(), typeof(Interface1));

}

Here's the CPP shim code (that matters):

void *CreateInstance()

{

return (void *)ClassLibrary1::Class1().CreateInstance();

}

Here's the .def code:

LIBRARY "CppClassLibrary1"

EXPORTS

CreateInstance @1

Make sure that the C# types are marked ComVisible(True). You should be able to cast the void * to the interface definition (they should be the same on either side...)

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dllexport in C#