Question

I’m trying to come up with a solution as to how I can pass an array of arrays from C# into a native function. I already have a delegate to the function (Marshal.GetDelegateForFunctionPointer), but now I’m trying to pass a multidimensional array (or rather; an array of arrays) into it.

This code example works when the input has 2 sub-arrays, but I need to be able to handle any number of sub-arrays. What’s the easiest way you can think of to do that? I’d prefer not to copy the data between arrays as this will be happening in a real-time loop (I’m communicating with an audio effect)

public void process(float[][] input)
{
    unsafe
    {
        // If I know how many sub-arrays I have I can just fix them like this... but I need to handle n-many arrays
        fixed (float* inp0 = input[0], inp1 = input[1] )
        {
            // Create the pointer array and put the pointers to input[0] and input[1] into it
            float*[] inputArray = new float*[2];
            inputArray[0] = inp0;
            inputArray[1] = inp1;
            fixed(float** inputPtr = inputArray)
            {
                // C function signature is someFuction(float** input, int numberOfChannels, int length)
                functionDelegate(inputPtr, 2, input[0].length);
            }
        }
    }
}

Answer 1

You can pin an object in place without using fixed by instead obtaining a pinned GCHandle to the object in question. Of course, it should go without saying that by doing so you take responsibility for ensuring that the pointer does not survive past the point where the object is unpinned. We call it “unsafe” code for a reason; you get to be responsible for safe memory management, not the runtime.

http://msdn.microsoft.com/en-us/library/system.runtime.interopservices.gchandle.aspx