Question

I’m using C++/CLI only to unit test unmanaged C++ code in VS2010. I switched the compiler to /clr and using the unmanaged code from a static library.

I have a simple int property in my test class.
I would like to pass that as a const int & to a function in native C++. But it can’t compile and I’ve found out that, it’s because you can’t mix references like that.

What is the way to do it, I tried to following and it’s working, but is there a nicer way?

[TestClass]
public ref class MyTestClass
{
private:
    int _my_property;
public:

    [TestMethod]
    void MyTestMethod()
    {
        MyNativeClass c;
        // c.SomeMethod(_my_property) this doesn't work

        int i = _my__property;
        c.SomeMethod(i) // this works
    }
}

Answer 1

C++ references are really just syntactic sugare for pointers. A C++ pointer points to a specific point in memory, while CLI references can be freely moved around by the garbage collector. To pass a reference to an object in managed memory to unmanged code, you need to pin the pointer.

More info and sample in another SO question: Convert from C++/CLI pointer to native C++ pointer

Edit 2

I’m removing the additional information, since it is obviously wrong (thanks @Tergiver and @DeadMG for your comments). I’m also making the post community wiki, so feel free to add any additional correct information.