Marshall array of structures

Question

I've spent a lot of time to look for the solution but still don't find it out.

I have 2 classes:

[StructLayout(LayoutKind.Sequential)]
public class Result
{
    public int Number;
    [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 4)]
    public string Name;
    public int Size;
}

[StructLayout(LayoutKind.Sequential)]
public class CoverObject
{
    public int NumOfResults;
    [MarshalAs(UnmanagedType.ByValArray, ArraySubType = UnmanagedType.Struct, SizeConst = 4)]
    public Result[] Results;
}

My expectation that the command Marshal.SizeOf(typeof(CoverObject)) will return 52, but not, it's just 20. Thus, all of marshall and unmarshall that I use later are not working.

Seeming it only counts the first member (Number) in Result class. Did I do anything wrong?

Answer 1

Change your classes to structs

[StructLayout(LayoutKind.Sequential)]
public struct Result
{
    public int Number;
    [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 4)]
    public string Name;
    public int Size;
}

[StructLayout(LayoutKind.Sequential)]
public struct CoverObject
{
    public int NumOfResults;
    [MarshalAs(UnmanagedType.ByValArray, ArraySubType = UnmanagedType.Struct, SizeConst = 4)]
    public Result[] Results;
}

some where else:

Marshal.SizeOf(typeof(CoverObject)) // it will return 52