Question

So as the title states, I am looking to pass an object that is defined in an unmanaged C++ project into a managed C++/CLI project (both projects are in the same solution) while still being able to access the same methods as in the unmanaged C++ project.

This object is a class which imports functions from a separate unmanaged C++ dll (not in the same project or solution) through the means of using typedef‘s as shown below (excerpt of header):

#pragma unmanaged    

typedef BOOL (WINAPI *someBoolFunc) (DWORD Name, DWORD Flags, TCHAR* Text);

class INeedThisClass
{
public:
    INeedThisClass();
    ~INeedThisClass();

    someBoolFunc BoolFunc;
}; 

extern INeedThisClass ReallyNeedThisClass;

I would really like to be able to access the externed object ReallyNeedThisClass from within my managed code by just only passing the object. By having this object I wish to access it’s methods through ReallyNeedThisClass->BoolFunc. What is the best way of accessing this object from my managed code?

EDIT: I’ve been thinking maybe there is a way of using a property to “Get” the object from the unmanaged code and then “Set” the same object in the managed code. Could this be a proper angle to approach this issue from? I’ve cleaned up the question a bit to get rid of useless details.

UPDATE: I’ve made progress on this using a wrapper for the unmanaged C++ code, but of course there are still problems. Using the above class as an example here, I will show you what I have managed to do up until now.

Project 1: Unmanaged C++ class (example above)

Project 2: Managed C++/CLR wrapper class (example below)

Wrapper.h:

#pragma once

#include "INeedThisClass.h" //Unmanaged class INeedThisClass

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

namespace INeedThisClassWrapper
{
    public ref class INTC
    {
    public:
        INTC(void);
        virtual ~INTC(void);

        delegate bool BoolFunc(UInt32 Name, UInt32 Flags, String^ Text);

    private:
        INeedThisClass *ReallyNeedThisClass;
    };
}

Wrapper.cpp:

#include "Stdafx.h"
#include "Wrapper.h"
using namespace INeedThisClassWrapper

#include <msclr/marshal.h>
using namespace msclr::interop;

INTC::INTC(void)
{
    ReallyNeedThisClass = new INeedThisClass();
}

INTC::~INTC(void)
{
    if (ReallyNeedThisClass)
    {
        delete ReallyNeedThisClass;
        ReallyNeedThisClass = NULL;
    }
}

bool INTC::BoolFunc(UInt32 Name, UInt32 Flags, String^ Text)
{
    return ReallyNeedThisClass->BoolFunc;
}

Now I am receiving errors from the compiler stating:

error C2065: 'WINAPI': undeclared identifier
error C2065: 'someBoolFunc': undeclared identifier
error C4430: missing type specifier - int assumed. Note C++ does not support default-int

Any ideas?

Answer 1

First, you have to export INeedThisClass from unmanaged dll and import from managed one.

//unmanaged header

#if UNMANAGED_COMPILE_DEFINITION
#define EXPORT_OR_IMPORT __declspec(dllexport)
#else
#define EXPORT_OR_IMPORT __declspec(dllimport)
#endif

class EXPORT_OR_IMPORT INeedThisClass
{
public:
    INeedThisClass();
    ~INeedThisClass();

    someBoolFunc BoolFunc;
};

Also unmanaged dll must be compiled with UNMANAGED_COMPILE_DEFINITION preprocessor definiton.

Second, remove extern INeedThisClass ReallyNeedThisClass; you don’t need it. Because ReallyNeedThisClass is a member of wrapper class already.

Third, you need to marshal System::String^ to TCHAR* in order to call BoolFunc

Forth, I do not remember but if you include “Windows.h” or “Winnt.h”, the error about WINAPI will be gone.