passing a struct through a namedpipe

Hi. I got a problem with a program made up with 2 modules. The 1st written in C++ that generates data and the 2nd one that reads data. The transmission take place through a NamedPipe that transport data from "c++" to "c#". Data are in form of structure.
Sending a simple integer isn't a problem but when I try to send a struct, i got a problem in the C# module that seems not able to transform data in the read buffer to the original struct.
This is a simplified code i wrote:

C++ SIDE

npipe = CreateFile("\\\\.\\pipe\\TestChannel",
                       GENERIC_READ | GENERIC_WRITE,
                       0, NULL, OPEN_EXISTING, 0, NULL);

 struttura _s;
      _s.numero = 12;
      
      WriteFile(npipe, &_s, sizeof(struttura), &bread, NULL)

C# SIDE

[StructLayout(LayoutKind.Sequential)]
        public struct struttura {
            public int numero;
        }


FileStream fStream = new FileStream(clientPipeHandle, FileAccess.ReadWrite, BUFFER_SIZE, true);
                    byte[] buffer = new byte[BUFFER_SIZE];
                    ASCIIEncoding encoder = new ASCIIEncoding();
                    struttura _s;
                    _s.numero = -1;
                    fStream.Read(buffer, 0, System.Runtime.InteropServices.Marshal.SizeOf(_s.GetType()));
                    IntPtr i = (IntPtr) System.Runtime.InteropServices.Marshal.SizeOf(_s);
                    _s = (struttura) System.Runtime.InteropServices.Marshal.PtrToStructure(i ,_s.GetType());