sizeof structure at compile time

[AliSmith]

Hi,

I'm new to C#, and am converting a C++ app which interfaces with a legacy Delphi app. We pass messages between the two apps over UDP, and my colleague is writing a conversion utility to take his Delphi message structure definitions and produce the equivalent in C#. However we have hit upon several issues, which I can't find a way round. The main one seems though to be when using the size of a previously defined message structure to define a constant for use elsewhere. So, in Delphi we have:

type
  T_UDP_pkt = array[0..MAX_UDP_PACKET_SIZE - 1] of char;
  T_UDP_header = packed record
    From_MAC: T_MAC;
    From_Area_ID: word; // 0= PC
    Signature: array[0..5] of char;
    Pkt_count: word; // Total number of packets in this set
    Pkt_number: word; // Packet Number
    Transaction: longword;
    spare1: array[0..5] of byte;
    AC_to_AC: array[0..3] of byte;
    datalen: longword; // length of data block following header
    Code: longword;
    Last_received_transaction: longword;
    Hash: TDigest;
    AC_WAN_Port: word;
    Spare2: array[0..7] of byte;
  end;
const MAX_UDP_DATA_SIZE = (sizeof(T_UDP_pkt) - sizeof(T_UDP_header));

I've managed to create the T_UDP_pkt and T_UDP_Header strutures in C# with

[StructLayout(LayoutKind.Sequential, Pack = 1)]

and
[MarshalAs(UnmanagedType.ByValArray, SizeConst = x)] commands,

but I can't define the constant MAX_UDP_DATA_SIZE as if I use

Marshal.Sizeof(T_UDP_pkt) 

I get an error about using a type when a variable is expected, or if I use

Marshal.Sizeof(typeof(T_UDP_pkt))

I get an error about the value not being constant. And if I use

sizeof(T_UDP_pkt)

I get an error saying I can't get the size of a managed type. Finally if I use

s

izeof(typeof(T_UDP_pkt))

I get an error that typeof(T_UDP_pkt) is not a type.

So I'm a bit stumped. Any help would be muich appreciated, as I'm sure it must be reasonably easy?!

[tlhintoq]

TIP: When you are writing your question, there is a button on the tool bar that wraps the [code] tags around your copy/pasted code. It helps a bunch. Its the button with a '#' on it. More on tags. They're cool. Check'em out.

[AliSmith]

Thanks, sorry about that, tlhintoq, next time!