Hi, not sure why I am getting all this, thanks anyway. some remarks: 1. either this struct has strict requirements or it has not. if it has, I doubt it should hold both public byte[] dataSenderBytes; and public string dataSender; // 12 same for public byte[] dataMessageBytes; and public string dataMessage; // 24 if it has not, don't see why it should need a Pack=1 attribute 2. your problem is with string handling. in the native world (C, C++) strings consist of 8-bit characters (or 16-bit wide characters) and they end on the first ASCII NULL character (byte value zero), which means the NULL character itself cannot be embedded in a string. in the managed world strings can contain any character you choose; if you give 12 bytes (dataSenderBytes) to ASCII.GetString() it probably returns a 12-character string of which several could be NULL (or \0). So I suggest you get the meaningful length of those strings somehow from the byte[] or from the native world, then use ASCIIEncoding.GetString(Byte[], 0, length) :) Luc Pattyn [Forum Guidelines] [My Articles] - before you ask a question here, search CodeProject, then Google - the quality and detail of your question reflects on the effectiveness of the help you are likely to get - use the code block button (PRE tags) to preserve formatting when showing multi-line code snippets

Just a note for anyone else who comes across this issue and sees this thread: The solution provided by Luc does NOT WORK with LayoutKind.Explicit, it only works with LayoutKind.Sequential, and with the FieldOffset()'s removed (obviously). This is the compiling + working code: [StructLayout(LayoutKind.Sequential, Pack = 1, Size = 66, CharSet = CharSet.Ansi)] public struct chatOne { public int packetType; //4 public int packetNumber; //4 public int packetSource; //4 public int packetDestination; //4 public short packetPort; // 2 public ushort packetInfoEnd; // 2 public byte dataId; // 1 \[MarshalAs(UnmanagedType.ByValTStr, SizeConst = 11)\] public string dataSender; // 11 public byte dataPadOne; // 1 \[MarshalAs(UnmanagedType.ByValTStr, SizeConst = 23)\] public string dataMessage; // 23 public short dataPart; // 2 public int dataEndCodeOne; // 4 public int dataEndCodeTwo; // 4 public chatOne(int dst, short port, string sender, string message) { packetType = 1192961; packetNumber = 0; packetSource = 0; packetDestination = dst; packetPort = IPAddress.HostToNetworkOrder(port); packetInfoEnd = 43521; dataId = 10; dataSender = sender; dataPadOne = 0; dataMessage = message; dataPart = 206; dataEndCodeOne = 10209786; dataEndCodeTwo = 6658; } }