How to use C# objects returned in QT.

Question

Hello everyone, Coming from .NET environment [VB & C#] with a beginner level in C++ and Qt and i was wondering is it possible to call methods from C# dll files in my Qt project.dll example:

namespace Calc;
public class Program{
      public int sum(int x,int y){
         return x+y;
      }
}

I want to use the sum sum method in my Qt C++ project. And in my Qt project would be like this

Program c;
c.sum(2+3);

Answer 1

In the event that Qt does not work well building with /clr you can refer to the following example.

C# class library -

using System;

namespace CSLibrary
{
    public class Class1
    {
        public int Add(int a, int b)
        {
            return a + b;
        }

        public int Subtract(int a, int b)
        {
            return a - b;
        }
    }
}

C++/CLI class library that wraps CSLibrary.dll -

#pragma once

#include <msclr\gcroot.h>

using namespace System;
#using <CSLibrary.dll>

namespace CppWrapLibrary {
    class CppWrap
    {
    public:
        virtual int Add(int a, int b) = 0;

        virtual int Subtract(int a, int b) = 0;

        virtual ~CppWrap() = default;
    };

    class CppWrapImpl : public CppWrap
    {
    public:
        virtual int Add(int a, int b)
        {
            return m_CSref->Add(a, b);
        }

        virtual int Subtract(int a, int b)
        {
            return m_CSref->Subtract(a, b);
        }

        CppWrapImpl() : m_CSref(gcnew CSLibrary::Class1())
        {
        }

        // Included for debugging breakpoint instead of using compiler generated default destructor
        virtual ~CppWrapImpl()
        {
        };

    private:
        // m_CSref holds a reference to the C# class library.
        msclr::gcroot<CSLibrary::Class1^> m_CSref;
    };
};


// return a pointer to base class CppWrap.  CppWrapImpl cannot be declared in unmanaged code
__declspec(dllexport) CppWrapLibrary::CppWrap* CreateWrapper()
{
    return static_cast<CppWrapLibrary::CppWrap*>(new CppWrapLibrary::CppWrapImpl);
}

C++ console application that uses the C++/CLI DLL -

// CppConsole.cpp : This file contains the 'main' function. Program execution begins and ends there.
//

#include <iostream>

namespace CppWrapLibrary {
    class CppWrap
    {
    public:
        virtual int Add(int a, int b) = 0;

        virtual int Subtract(int a, int b) = 0;

        virtual ~CppWrap() = default;
    };
};

__declspec(dllimport) CppWrapLibrary::CppWrap* CreateWrapper();

using namespace CppWrapLibrary;

int main()
{
    CppWrap* pWrapper = CreateWrapper();
    if (pWrapper)
    {
        int x = pWrapper->Add(10, 10);
        int y = pWrapper->Subtract(100, 58);

        std::cout << "10 + 10 = " << x << "\n100 - 58 = " << y << std::endl;

        delete pWrapper;
    }
}

Answer 2

There are two general approaches to consuming managed code (C# class library) from unmanaged C++ code. The first approach is to create a class library using C++/CLI. This library serves as the intermediary between C++ and C#. An old but instructive example of this approach can be seen at Calling C# .NET methods from unmanaged C/C++. The second approach is for your C# class library to expose its objects and methods through COM.