How do I retrive information from this array?

Question

I have an IntPtr pointing to another IntPtr pointing to an unmanaged array. I was wondering how can I copy this unmanaged array to a managed one? I know I would have to use Marshal.Copy but I'm unsure of how to use it when I have a pointer to a pointer.

Here is my example code

Unmanaged C++:

void foo(Unsigned_16_Type**  Buffer_Pointer);

Managed C#:

[DllImport("example.dll")]
        public static extern void foo(IntPtr Buffer_Pointer);
//...
//...

int[] bufferArray = new int[32];


IntPtr p_Buffer = (IntPtr)Marshal.AllocCoTaskMem(Marshal.SizeOf(typeof(int)) * bufferArray.Length);
Marshal.Copy(bufferArray, 0, p_Buffer, bufferArray.Length);

GCHandle handle = GCHandle.Alloc(p_Buffer, GCHandleType.Pinned);
IntPtr ppUnmanagedBuffer = (IntPtr)handle.AddrOfPinnedObject();

//Call to foo
foo(ppUnmanagedBuffer);

So now at this point I have a IntPtr to an IntPtr to an array inside ppUnmanagedBuffer but I'm unsure of how to copy that array over to a new managed one using Marshal.Copy

I tried something like

int[] arrayRes = new int[word_count];
Marshal.Copy(ppUnmanagedBuffer, arrayRes, 0, word_count);

But that does not work

Answer 1

The only thing remaining is to "undo" the following calls to get ppUnmanagedBuffer to point to the type of data you are expecting:

GCHandle handle = GCHandle.Alloc(p_Buffer, GCHandleType.Pinned);

IntPtr ppUnmanagedBuffer = (IntPtr)handle.AddrOfPinnedObject();

If C# has managed to give you the equivalent of int** by this mechanism, then you need to dereference it once to get an equivalent to int[] , like so:

Marshal.Copy((IntPtr)(GCHandle.FromIntPtr(ppUnmanagedBuffer).target), arrayRes, 0, word_count);

(The syntax may be off a bit, but that's the general idea...)