passing by reference from unmanaged c++ -> c++/CLI -> c#

[acastrucc]

I have a third party unmanaged c++ library.
I created a managed c++ wrapper for it since I need to call it from c# code. Problem is one of native c++ functions passes an int by reference. I do not know how to route this through the managed wrapper to the c# code. For example

class A //unmnaged SDK class
{
public:
void Foo(int& i);
}

//managed c++ wrapper
public ref class A_Wrapper
{
public:
A_Wrapper() {_unmanaged = new A();};
~A_Wrapper() {delete unmanaged; };
void Foo(int& i) { _unmanaged->Foo(i)};
private:
A * _unmanaged;
}

In my c# (yes #) code I try to call A_Wrapper::Foo() but I get compile errors

c# code:
public static void Main()
{
A_Wrapper aw = new A_Wrapper();
int id = 0;
aw.Foo(&id);
}
error CS0214: Pointers and fixed size buffers may only be used in an unsafe context

I don't really want to wrap it in an unsafe {} block. How do I route the pass by reference from c++ to c# properly?

[Eri523]

I'd suggest you introduce a "shadow variable" for the parameter in your managed wrapper, pass in the variable as a tracking reference from your C# code (don't know the C# syntax for that, though), assign it to the shadow variable and then assign it back after calling the wrapped native function.

Somewhat like this:

// Test25.cpp: Hauptprojektdatei.

#include "stdafx.h"

using namespace System;

class A //unmnaged SDK class
{
public:
  void Foo(int& i) { ++i; }
};

//managed c++ wrapper

public ref class A_Wrapper 
{
public:
  A_Wrapper() { _unmanaged = new A; }
  ~A_Wrapper() { delete _unmanaged; }

  void Foo(int% i)
  {
    int wrapper_i = i;
    _unmanaged->Foo(wrapper_i);
    i = wrapper_i;
  }

private:
  A * _unmanaged;
};

int main(array<System::String ^> ^args)
{
  A_Wrapper ^wrapper = gcnew A_Wrapper;
  int i = 1;
  wrapper->Foo(i);
  Console::WriteLine(i);  // Will print 2
  Console::ReadLine();
  return 0;
}

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