Question

I am working on a solution, most of its core engine is developed as Win32 C++ (and is Platform independent and is also used on OS X), some time ago we needed to call C++ dll’s of core engine from C# and I was able to Load main solution’s DLL in C# (by the help of some threads here on SO). but now we have certain things implemented in Managed C# dll and need to use it in Win32 C++ project? (and just function definitions and dll are provided)

Answer 1

You can create a managed C++ interop DLL to act as a wrapper around the C# library.

Most tutorials on managed C++ unfortunately only explain how to wrap unmanaged C++ for use in C#. But it can work the other way also.

Define an abstract interface class in your native C++ code, then create a concrete subclass inside the managed C++ DLL. Call into your C# objects in the method implementations.

Finally, export a factory function that will instantiate the implementation class and return a base-class pointer that your native code can use.

Here’s a quick example:

First, define the class interface in your native DLL.

interopclassbase.h

class InteropClassBase
{
public:
    virtual void doStuff() = 0;
    virtual int getValue() = 0;
    virtual void getString(CString* outStr) = 0;
};

Now you need to create a C++/CLI DLL that will allow you to mix native and managed code in a single assembly. Add a new C++ project to your solution, and in the project configuration set the “Common Language Runtime Support” option to Mixed (/clr).

Once you’ve added a reference to your C# library (which we’ll call ManagedLibrary) we can implement the interop class:

interopclass.cpp

#include "interopclassbase.h"
#include <vcclr.h>

public class InteropClass : public InteropClassBase
{
protected:
    gcroot<ManagedLibrary::ManagedObject^> m_managedObject;

public:
    InteropClass()
    {
        m_managedObject = gcnew ManagedLibrary::ManagedObject();
    }

    virtual void doStuff()
    {
        m_managedObject->doStuff();
    }

    virtual int getValue()
    {
        return m_managedObject->getValue();
    }

    virtual void getString(CString* pOutStr)
    {
        System::String^ managedString = m_managedObject->getString();
        CString nativeString(managedString); // overloaded CString constructor
        if (pOutStr) *pOutStr = nativeString;
    }
};

__declspec(dllexport) InteropClassBase* getImplementationPointer()
{
   return new InteropClass();
}

Now you just need to load the interop DLL from your native project and call the exported function.