Memory allocated with C++ and Marshall to C#

Question

What happens when I allocate memory (structs within double pointer) in C++ and use it via Marshall with C#?

Do I have to clean up the memory or does the C# GarbageCollection do it for me? Marshall.FreeHGlobal(vsResult); doesn't work.

[StructLayout(LayoutKind.Sequential)]
public struct MyCppResults
{
    [MarshalAs(UnmanagedType.I4)] public int ResultSize;
    public unsafe double* Result;
}

[DllImport("SomeVeryFastAlgorithm.dll")]
public  static extern double[] LoadResults()
{
    var resultsPtr = GetResults();
    var vsResult = Marshal.PtrToStructure<MyCppResults>(resultsPtr);
    var resultMatrix = new double[vsResult.ResultSize];
    unsafe
    {
        for (var i = 0; i < resultMatrix.Length; i++)
            resultMatrix[i] = vsResult.Result[i];
    }
    return resultMatrix;
}

Answer 1

As Marshall.FreeHGlobal notes, this works in conjunction with AllocHGlobal . It doesn't work in conjunction with C++ new[] .

The memory allocated by new[] is almost certainly allocated by the C++ Standard Library (if not, it's owned by a user-defined override). This must be returned by delete[] .

You can call back from C# to C++ to tell it to call delete[] . A logical location would be the C# destructor (finalizer).