Accessing nested structs in C# with LayoutKind.Explicit

I have an application in C# that needs to share some binary data with Python, and I'm planning to use shared memory (memory mapped file). Thus, I need to have the same binary structure on both sides.

I create a struct in C# (ST_Layer) that has an array of items of another struct (ST_Point). To access those items I have defined a function getPoint that will return a pointer to the position of the requested ST_Point.

using System.Diagnostics;using System.Runtime.InteropServices;using System.Threading;class TestProgram{    [StructLayout(LayoutKind.Explicit, Pack = 8)]    public struct ST_Point    {        [FieldOffset(0)] public double X;        [FieldOffset(8)] public double Y;    }    [StructLayout(LayoutKind.Explicit, Pack = 8)]    public unsafe struct ST_Layer    {        [FieldOffset(0)] public ushort nPoints;        [FieldOffset(8)] public double fHeight;        [MarshalAs(UnmanagedType.ByValArray, SizeConst = 10)]        [FieldOffset(16)] public ST_Point[] Points;        public unsafe ST_Point* getPoint(int n)        {            fixed (ST_Layer* thisPtr = &this)            {                int ptr = (int)&(thisPtr->Points) + n * ((16 + 3) / 4) * 4;   // Sizeof ST_Point 16                return (ST_Point*)ptr;            }        }    }    static void Main(string[] args)    {        unsafe        {            ST_Layer layer = new ST_Layer();            layer.nPoints = 3;            layer.fHeight = 4;            layer.getPoint(0)->X = 5;            layer.getPoint(3)->Y = 6;            for (int i = 0; i < 10; i++)                Debug.WriteLine("Data [" + i +"] " + layer.getPoint(i)->X +", " + layer.getPoint(i)->Y +" - ");            while (true)                Thread.Sleep(50);        }    }}

I have 2 questions:

• The previous code works if I compile the code for x86, but not for x64 or 'Any CPU' ('System.AccessViolationException' exception in 'layer.getPoint(0)->X'). Is it an expected behaviour? What can I do to solve this exception?
• I'm using the getPoint function to access the ST_Point array because I have not seen a better way of accessing it. Is it possible to access it as a normal array (i.e. layer.Points[0].X)? I can't create the array of ST_Point (layer.Points = new ST_Point[10]), as it'll be created outside the ST_Layer, and data will not be passed to Python.

I've seen this and this, but don't know how to access the individual fields of ST_Point.

Thank you for your help.

[Also, thank you R. Martinho Fernandes for your hint regarding the x86/x64 issue]