How do I convert a cli::array to a native array from native code?

Question

I'm writing a native wrapper around a managed component written in C++\CLI.

I have the following function in managed code:

array<Byte>^ Class::Function();

I want to expose this function from a native C++ class with the following signature:

shared_array<unsigned char> Class::Function();

I've gotten as far as calling the managed function from native code, but I'm not sure how to safely copy the managed array into an unmanaged one.

gcroot<cli::array<System::Byte>^> managedArray = _managedObject->Function();

Answer 1

There are two usual approaches:

1. Perform the marshaling with native code, which requires use of pin_ptr<>:

   boost::shared_array<unsigned char> convert(array<unsigned char>^ arr)
   {
       boost::shared_array<unsigned char> dest(new unsigned char[arr->Length]);
       pin_ptr<unsigned char> pinned = &arr[0];
       unsigned char* src = pinned;
       std::copy(src, src + arr->Length, dest.get());
       return dest;
   }
   

2. Perform the marshaling with managed code, which requires use of the Marshal class:

   boost::shared_array<unsigned char> convert(array<unsigned char>^ arr)
   {
       using System::Runtime::InteropServices::Marshal;
   
       boost::shared_array<unsigned char> dest(new unsigned char[arr->Length]);
       Marshal::Copy(arr, 0, IntPtr(dest.get()), arr->Length);
       return dest;
   }
   

Generally I would prefer the latter approach, as the former can hinder the GC's effectiveness if the array is large.

Answer 2

Take a look at pin_ptr, it lets you pass address of a managed class to an unmanaged function.