Passing a managed Object as parameter in C /CLI Wrapper Function to be exported to native Win32 dll

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C++

C++/CLI

C#

Good morning,
I am working on a project which combine C++ dll and C#. I have to make a kind of bridge between both. Now, I have to call C# functions inside C++ dll. for doing that, I made a C/ClI wrapper.
My project is divided in several parts :

- My C# code :
The file Class1.cs

namespace ManagedClasses
{
  public class MessageShower
  {
    private string _message = "";

    public MessageShower()
      : this("TEST WRAPPER")
    {
    }

    public MessageShower(string message)
    {
      _message = message;
    }

    public void CreateArea(Area areaTest, Point pt1 , Point pt2, string message)
    {
      message = "Creation of area";
      Console.WriteLine(message);

      pt1 = new Point(2, 3);
      pt2 = new Point(4, 8);

      areaTest = new Area(pt1, pt2);
      Console.WriteLine("Area created");
      Console.WriteLine("Details of area :");
      Console.WriteLine(" -> BottomRight pt1({0},{1})", pt1.GetX(), pt1.GetY() );
      Console.WriteLine(" -> BottomRight pt2({0},{1})", pt2.GetX(), pt2.GetY() );

    }
    public int AddXPoints(Point a, Point b)
    {
      return (a.GetX() + b.GetX());
    }
    public void Show()
    {
      Console.WriteLine("Message Test : {0}", _message);
    }

    public int Add(int first, int second)
    {
      return first + second;
    }
  }
}

The file Class2.cs

namespace WrapperTest
{
  public class Area 
  {
    public Area(Point pt1, Point Pt2)
    {
      BottomRight.SetX(pt1.GetX());
      BottomRight.SetY(pt1.GetY());

      TopLeft.SetX(Pt2.GetX());
      TopLeft.SetY(Pt2.GetY());
    }

    private Point BottomRight;
    private Point TopLeft;
  }

  public class Point
  {
    public Point() : this(0, 0) { }

    public Point(int a , int b)
    {
      x = a;
      y = b;
    }

    public void SetX(int a) { x = a; }
    public void SetY(int b) { y = b; }
    public int GetX() { return x; }
    public int GetY() { return y; }

    public void DisplayPoint()
    {
      Console.Write("Point : x({0}) , y({1})", x, y);
    }
    private int x;
    private int y;
  }
}

- My C\CLi wrapper use 3 C++ files :
The first one CLIWrapper.h :

using namespace ManagedClasses;
using namespace System::Runtime::InteropServices;
using namespace abstractWrapper;


namespace CliWrapper
{
  public ref class Cli
  {
    Cli(void)
    {
      managedObject = gcnew MessageShower();
    }

    ~Cli()
    {
      delete CliInstance;
    }

  public :
    MessageShower^ managedObject;
    static Cli^ CliInstance = gcnew Cli();
  };
}

The .cpp files associated to the header : CLIWrapper.cpp

#include "CLIWrapper.h"
#include "NativeInterface.h"


namespace CliWrapper
{
#ifdef __cplusplus
extern "C"
{
#endif
    __declspec(dllexport) void DisplayTest()
    {
      Cli::CliInstance->managedObject->Show();
    }

    __declspec(dllexport) int AddTest(int first, int second)
    {
      System::Int32 paramFirst = first;
      System::Int32 paramSecond = second;
      System::Int32 returnVal = Cli::CliInstance->managedObject->Add(paramFirst, paramSecond);
      return returnVal;
    }
#ifdef __cplusplus
}
#endif
}

The file concerning the declaration of the function which be called in C++ dll : NativeInterface.h :

#ifdef __cplusplus
extern "C"
{
#endif
  __declspec(dllexport) void DisplayTest();
  __declspec(dllexport) int AddTest(int first, int second);
#ifdef __cplusplus
}
#endif

I test it in a main program in C++ and I can call the function DisplayTest and AddTest.

Now I would like to do the same with the function CreateArea (in Class1.cs in C#). For doing the same thing, I have to transform C# object like Area , Point to unmanaged types which can be understood by C++ and I don't know how to do it.
So I would like to know if someone have an idea to do that.

Thanks in advance.