Invoking C# WPF code in C++

Question

thsi is my first time asking a question here, althought i use this site a lot!!

So after I've searched a while, i found this: http://tigerang.blogspot.pt/2008/09/reverse-pinvoke.html

I think that is almost what i want to do. I will now explain: (PLZ note i'm new to c++, c#, i come from java)I have a solution on visual studio with two projects, unmanaged c++ and a C# WPF app. The c++ only has one class, that does some processing using OpenCV. The WPF class connects to an image, retrieves some (x,y) points, and i have to pass them to c++. Afterwards I will call a C++ function from the WPF side, where i will get my results.

SO my question now is, I want to pass a List of Points (List), but i'm having trouble adapting the example I'm seeing to my situation and i found very litle documentation on this (or perhaps i'm too newbie and i don't know how to find/use it).

Sample code: C#

[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode)]
public struct Ponto
{
    public double x;
    public double y;
}


[UnmanagedFunctionPointer(CallingConvention.Cdecl)]
public delegate List<Ponto> CallBackDelegate();



public class ManagedClass
{
    private CallBackDelegate _delegate;



    public List<Ponto> vectorp;

    public ManagedClass()
    {
        _delegate = new CallBackDelegate(this.Foo);
    }

    public CallBackDelegate GetDelegate()
    {
        return _delegate;
    }

    public List<Ponto> Foo()
    {
       //do shit
        Ponto p1 = new Ponto();
        p1.x = 10;
        p1.y = 2;
        Ponto p2 = new Ponto();
        p2.x = 5;
        p2.y = 7;
        Ponto p3 = new Ponto();
        p3.x = 3;
        p3.y = 8;
        vectorp.Add(p1);
        vectorp.Add(p2);
        vectorp.Add(p3);


        return vectorp; 
    }
}

---

SAmple Code C++;

 #include <iostream>

 #pragma once
 #include <windows.h>
 #include <list>


 #define INTEROPBRIDGE_API __declspec(dllexport)

 INTEROPBRIDGE_API void fnInteropBridge(list<Ponto> data) //IM GETTING ERRORS HERE
 {
     ManagedLib::ManagedClass^ c = gcnew ManagedLib::ManagedClass();
     IntPtr p = Marshal::GetFunctionPointerForDelegate(c->GetDelegate());

     NativeToManaged funcPointer = (NativeToManaged) p.ToPointer();

     // invoke the delegate
     funcPointer(data);
 }


 // data structure for the callback function
 struct Ponto
 {
     double x;
     double y;
 };

 // callback function prototype
 typedef void (*NativeToManaged)(list<Ponto> data);

 using namespace std;
 void main()
 {
   cout << "Hello World!" << endl;   
   cout << "Welcome to C++ Programming" << endl;

 }

Answer 1

Your C++ code won't work because System.Collections.Generic.List is completely different from C++'s std::list.

If your C++ code is managed (as it currently is), you can just reference the C# classes directly. No need for function pointers.

But if you really want to consume C# code from unmanaged C++, the simplest way is through COM. The only thing you need to change about your C# code is to change ManagedClass.Foo to return an array instead of a List, because List is not visible to COM, plus add a couple of attributes to the types and add an interface for the class to implement:

[ComVisible(true)]
[Guid("2EF06BCB-A25B-41AD-B233-33A956DBEB69")]
public struct Ponto
{
    public double x;
    public double y;

    public Ponto(double x, double y)
    {
        this.x = x;
        this.y = y;
    }
}

[ComVisible(true)]
[Guid("EB9258F5-DCFB-4F91-8342-5A05EB17557D")]
public interface IManagedClass
{
    Ponto[] Foo();
}

[ComVisible(true)]
[Guid("11B23AD7-F79E-45D7-BC87-89F0DBC8B83F")]
[ClassInterface(ClassInterfaceType.None)]
public class ManagedClass : IManagedClass
{
    private List<Ponto> points;

    public ManagedClass()
    {
        points = new List<Ponto>();
        points.Add(new Ponto(1.0, 1.0));
        points.Add(new Ponto(2.0, 2.0));
        points.Add(new Ponto(3.0, 3.0));
    }

    public Ponto[] Foo()
    {
        return points.ToArray();
    }
}

Build the project, start the Visual Studio Command Prompt with administrator privileges, and use a command like this to export a type library for the assembly and register it:

regasm ManagedAssembly.dll /tlb:ManagedAssembly.tlb /codebase

And the C++ code would consume it like this:

#import "ManagedAssembly.tlb"
#include <iostream>

using namespace ManagedAssembly;
using namespace std;

int main()
{
    ::CoInitialize(NULL);

    {
        IManagedClassPtr pManagedClass(__uuidof(ManagedClass));

        SAFEARRAY* psa = pManagedClass->Foo();
        Ponto* pPoints = (Ponto*)psa->pvData;

        for (int i = 0; i < 3; ++i)
            cout << pPoints[i].x << " " << pPoints[i].y << endl;
    }

    ::CoUninitialize();
}