Marshal.Copy by copying an IntPtr array to IntPtr

Question

I can’t understand how the method works Copy(IntPtr[], Int32, IntPtr, Int32). I could copy the data contained in several IntPtrs into one IntPtr (as MSDN states), but apparently it does not work as I expected:

IntPtr[] ptrArray = new IntPtr[]
{
    Marshal.AllocHGlobal(1),
    Marshal.AllocHGlobal(2)
 };

 Marshal.WriteByte(ptrArray[0], 0, 0xC1);

 // Allocate the total size.
 IntPtr ptr = Marshal.AllocHGlobal(3);

 Marshal.Copy(ptrArray, 0, ptr, ptrArray.Length);

 // I expect to read 0xC1 but Value is always random!!
 byte value = Marshal.ReadByte(ptr, 0);

Does anyone know if I use this method for something that is not its purpose?

Answer 1

    static void Main(string[] args)
    {
        IntPtr[] ptrArray = new IntPtr[]
        {
            Marshal.AllocHGlobal(1),
            Marshal.AllocHGlobal(2)
        };

        Marshal.WriteByte(ptrArray[0], 0, 100);

        int size = Marshal.SizeOf(typeof(IntPtr)) * ptrArray.Length;
        IntPtr ptr = Marshal.AllocHGlobal(size);

        Marshal.Copy(ptrArray, 0, ptr, ptrArray.Length);

        // Now we have native pointer ptr, which points to two pointers,
        // each of thme points to its own memory (size 1 and 2).

        // Let read first IntPtr from ptr:
        IntPtr p = Marshal.ReadIntPtr(ptr);

        // Now let read byte from p:
        byte b = Marshal.ReadByte(p);

        Console.WriteLine((int)b);    // prints 100

        // To do: release all IntPtr
    }

Read the explanation in the comments.