Hello,

I have a C# managed dll which I want to call from unmanaged C++.
For this I've exposed the functions from the C# code with COM. The code
is printed below.

I have a c# function 'PrintRef' which takes a string as a ref argument
and fills it with an arbitrary value.
However, when C++ calls the 'PrintRef(ref string name)' function, I get
a runtime error.

I don't really understand what is happening here and why it happens.
Can somebody give some insights?

Regards,
Gerben

### C++ code ###

#include "stdafx.h"
#import <mscorlib.tlb> raw_interfaces_only
#import "CSharpServer.tlb" no_namespace named_guids

int main(int argc, char* argv[])
{
    CoInitialize(NULL);

    IManagedInterface *cp = NULL;

    HRESULT hr = CoCreateInstance(CLSID_InterfaceImplementation,
        NULL, CLSCTX_INPROC_SERVER,
        IID_IManagedInterface, reinterpret_cast<void**>(&cp));

    cp->PrintHi("Gerben");

    BSTR *bstrname = new BSTR();
    cp->PrintRef(bstrname);

    // Be a good citizen and clean up COM:
    CoUninitialize();
    return 0;
}
###

### C# code ###
using System;
using System.Runtime.InteropServices;

namespace CSharpServer
{
    // Since the .NET Framework interface and coclass have to behave as
    // COM objects, we have to give them guids.
    [Guid("DBE0E8C4-1C61-41f3-B6A4-4E2F353D3D05")]
    public interface IManagedInterface
    {
        int PrintHi(string name);
        void PrintRef(ref string name);
    }

    [Guid("C6659361-1625-4746-931C-36014B146679")]
    public class InterfaceImplementation : IManagedInterface
    {
        public int PrintHi(string name)
        {
            Console.WriteLine("Hello, {0}!", name);
            return 33;
        }

        public void PrintRef(ref string name)
        {
            name = "123gerben";
        }
    }
}
###