Managed C++, passing arguments by reference

Hi there,
To quickly ilustrate my problem, say I got a ref class that's creating a window, with some variable as well as handle to second window which should modify mentioned variable, eg:

Code:

---

public ref class Window1 : public System::Windows::Forms::Form
{
  private:
    int var;
    Window2^ win;
// ...
}

---

;

And now, how to pass reference to var to some Window2 method or constructor?
When I'm doing it this way:

Code:

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Window2::someMethod(int& ref);
Window1->Window2->someMethod( var );

---

I'm getting this error

Code:

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An object from the gc heap (member of a managed class) cannot be converted to a native reference

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The error message itself explains what's going on quite much, but for some reasons I couldn't find answer how to solve it (or maybe I got it all wrong).

(I know I could use ->get() method as for single variable, but in real program I'm using more variables, that's why I thought references might come in handy... Maybe I should wrap them in some class and try to work with passing pointers? But still, how to do it using references is what's bugging me.)

Just pass ints by values since there isnt much difference in preformance.

Well, I need original values to be modified, and passing by value won't help then. Question that remains unaswered is, how to pass managed class data by reference, if that's even possible. (as for now I wrapped my parameters into class and I'm passing regular class pointer, which works but I don't think it's nice solution).

Quote:

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Originally Posted by jimzy

Well, I need original values to be modified, and passing by value won't help then. Question that remains unaswered is, how to pass managed class data by reference, if that's even possible. (as for now I wrapped my parameters into class and I'm passing regular class pointer, which works but I don't think it's nice solution).

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I'm not up-to-date on all this "managed" crap but it seems like you can't really pass a "managed" variable by reference into unmanaged code, because the unmanaged code could change it and it would no longer be "managed."

Yes, it seems so. However, second window class (as in my example) is supposed to be managed too. Thing is, managed objects cannot by passed by native C++ reference (&) (even to managed class' own method [I know it's no point doing so, but still]), at least according to what I googled. Instead I should use some tracking references, handles, interior pointers and more which made me really confused and I didn't go much deeper into this... x.x Guess I'll just stick to pointers.

Cheers.

Quote:

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Originally Posted by jimzy

Yes, it seems so. However, second window class (as in my example) is supposed to be managed too. Thing is, managed objects cannot by passed by native C++ reference (&) (even to managed class' own method [I know it's no point doing so, but still]), at least according to what I googled. Instead I should use some tracking references, handles, interior pointers and more which made me really confused and I didn't go much deeper into this... x.x Guess I'll just stick to pointers.

Cheers.

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Why not copy the value into an unmanaged integer, pass a reference to that, then copy the resulting value back into the managed variable? I have no idea if that makes any sense -- like I said, I don't really know much about managed code.

Quote:

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Originally Posted by brewbuck

Why not copy the value into an unmanaged integer, pass a reference to that, then copy the resulting value back into the managed variable? I have no idea if that makes any sense -- like I said, I don't really know much about managed code.

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That's what I'm doing now, was just hoping somebody knows more "managed" solution to such problem :-)

Haven't looked at the facilities of C++/CLI closely, but wasn't there some way to fix gc-references and thus get a native reference/pointer to that thing?

Quote:

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Originally Posted by CornedBee

Haven't looked at the facilities of C++/CLI closely, but wasn't there some way to fix gc-references and thus get a native reference/pointer to that thing?

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Not sure if that's what you mean, but I run into something that solves the whole reference problem, let's say:

Code:

---

public ref class Foo
{
  int^ var;
  public:
      Foo()
      {
          var = gcnew int(10);
      }
      void modify(int^% ref)
      {
          ref = 20;
      }
};
// just a sample code, I know I could pass by value

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This does what regular '&' in native C++ would do, so seems like that's what I've been looking for.

Edit: oh, forgot to add (just in case somebody has similar problem and wants to go into details)
^ is gc managed heap object handle and
% is tracking reference

Cheers.