从C ++调用C＃COM DLL

Question

The C++ code is as follows

#include "stdafx.h"
#include <Windows.h>
#import "C:\shreyas\Documents\ConsoleApplication1\ConsoleApplication1\bin\Debug\ConsoleApplication1.tlb" no_namespace

int _tmain(int argc, _TCHAR* argv[])
{

    CoInitialize(NULL);
    IMyClassPtr obj;

    //iProgramPtr obj;
    obj.CreateInstance(__uuidof(MyClass));
    printf("value: %d",obj->display());
    CoUninitialize();
    getchar();

    return 0;
}

The C# code is as follows

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Runtime.InteropServices;
using System.Threading.Tasks;

namespace demo
{
    [ComVisible(true)]
    public interface IMyClass
    {
        int display();
    }


    [ComVisible(true)]
    [ClassInterface(ClassInterfaceType.None)]
    class MyClass : IMyClass
    {
        public int display()
        {
            Console.WriteLine("Hello");
            return 10;
        }
    }
}

I would like to call the C# display function from C++ code. I have done the required settings in C# project properties. In the code obj.CreateInstance(__uuid(MyClass)); the MyClass is giving an error as an undefined identifier.

Answer 1

Do pay attention to the build warning you get when you compile ConsoleApplication1:

warning MSB3214: "C:...\\ConsoleApplication1\\bin\\Debug\\ConsoleApplication1.dll" does not contain any types that can be registered for COM Interop.

That's not good of course. Also something you see with you look at the .tlb file with Oleview.exe's View + Typelib command. Or open the .tlh file that the #import directive generates with a text editor, find it back in the C++ project's Debug directory. You'll see that MyClass is completely missing, thus the compile error.

That is because of:

   class MyClass : IMyClass

You forgot to declare it public . Required.