Question

I have a large application written in native C++. I also have a class in C# that I need to call.

If the C# class was static, then it would be trivial (there’s lots of examples on the web) – just write the mixed C++/CLI wrapper, export the interfaces, and you’re done.

However, the C# class is non-static, and can’t be changed to static as it has an interface (the compiler will generate an error if you attempt to make the C# class static).

Has anyone run into this problem before – how do I export a non-static C# class to native C++?

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Update 2010-11-09

Final solution: tried COM, this worked nicely but didn’t support structures. So, went with a C++/CLI wrapper, because I absolutely needed to be able to pass structures between C++ and C#. I wrote a mixed mode .dll wrapper based on the code here:

• How to: Marshal Arrays Using C++ Interop

• How to: Marshal Structures Using C++ Interop

As the target class was non-static, I had to use the singleton pattern to make sure I was only instantiating one copy of the target class. This ensured everything was fast enough to meet the specs.

Contact me if you want me to post a demo project (although, to be fair, I’m calling C# from C++, and these days most people want to call C++ from C#).

Answer 1

C++/CLI or COM interop work just as well with non-static classes as with static. Using C++/CLI you just reference your assembly that holds the non-static class and then you can use gcnew to obtain a reference to a new instance.

What makes you think that this is not possible with your non-static class?

EDIT: there is example code here.

using namespace System;

public ref class CSquare
{
private:
    double sd;

public:
    CSquare() : sd(0.00) {}
    CSquare(double side) : sd(side) { }
    ~CSquare() { }

    property double Side
    {
    double get() { return sd; }
    void set(double s)
    {
        if( s <= 0 )
        sd = 0.00;
        else
        sd = s;
    }
    }

    property double Perimeter { double get() { return sd * 4; } }
    property double Area { double get() { return sd * sd; } }
};

array<CSquare ^> ^ CreateSquares()
{
    array<CSquare ^> ^ sqrs = gcnew array<CSquare ^>(5);

    sqrs[0] = gcnew CSquare;
    sqrs[0]->Side = 5.62;
    sqrs[1] = gcnew CSquare;
    sqrs[1]->Side = 770.448;
    sqrs[2] = gcnew CSquare;
    sqrs[2]->Side = 2442.08;
    sqrs[3] = gcnew CSquare;
    sqrs[3]->Side = 82.304;
    sqrs[4] = gcnew CSquare;
    sqrs[4]->Side = 640.1115;

    return sqrs;
}