Problem with Marshalling

[Yagirobi]

I have a C++ managed dll calling an unmanaged dll. The unmanaged dll has a
class library that I want to export. I'm having a problem with marshalling. I
reproduced the problem in a small example below. CBSTRUnmanaged is the
unmanaged class and ManagedBSTR is the managed class.

/*
Here's the unmanaged header file:
*/

#pragma once

class __declspec(dllexport) CBSTRUnmanaged
{
public:
CBSTRUnmanaged();
~CBSTRUnmanaged();
void SetCommPort(short nNewValue);
short GetFirmwareVersion(BSTR FAR* pSignature, BSTR FAR* pName, BSTR FAR*

pVersion);
};

/*
Here's the version of the unmanaged header file that I include in the managed

code:
*/

using namespace System;
using namespace System::Text;
using namespace System::Runtime::InteropServices;

class __declspec(dllimport) CBSTRUnmanaged

{
public:
CBSTRUnmanaged();
~CBSTRUnmanaged();
void SetCommPort(short nNewValue);
short GetFirmwareVersion([MarshalAs (UnmanagedType::BStr) ]StringBuilder*

pSignature,[MarshalAs (UnmanagedType::BStr) ]StringBuilder* pName,[MarshalAs

(UnmanagedType::BStr)]StringBuilder* pVersion);
};

/*
Here's the managed header file, its member function GetFirmwareVersion calls
the unmanaged GetFirmwareVersion:
*/


using namespace System;
#include "BSTRUnmanaged.h"
#pragma once

namespace ManagedBSTRspace
{
public __gc class ManagedBSTR
{
ManagedBSTR();
~ManagedBSTR();

short GetFirmwareVersion(StringBuilder* pSignature,StringBuilder* pName,

StringBuilder* pVersion);
void SetCommPort(short nNewValue);
CBSTRUnmanaged __nogc* unmanagedBSTRptr;
};
}

/*
The linker gives the error:

ManagedBSTR error LNK2001: unresolved external symbol "public: short

__thiscall CBSTRUnmanaged::GetFirmwareVersion(class

System::Text::StringBuilder __gc *,class System::Text::StringBuilder __gc

*,class System::Text::StringBuilder __gc *)"

(?GetFirmwareVersion@CBSTRUnmanaged@@$$FQAEFP$AAVStringBuilder@Text@System@@00

@Z)

*/

Why isn't MarshalAs changing the external parameter symbol from StringBuilder

to BSTR? Thanks.

Leon