How to convert a structure to a byte array in C

Question

How do I convert a structure to a byte array in C    I have defined a structure like this   public struct CIFSPacket       public uint protocolIdentifier    The value must be  0xFF  SMB        public byte command       public byte errorClass      public byte reserved      public ushort error       public byte flags         Here there are 14 bytes of data which is used differently among different dialects        I do want the flags2  However  so I ll try parsing them      public ushort flags2       public ushort treeId      public ushort processId      public ushort userId      public ushort multiplexId         Trans request     public byte wordCount   Count of parameter words defining the data portion of the packet        From here it might be undefined         public int parametersStartIndex       public ushort byteCount    Buffer length     public int bufferStartIndex       public string Buffer      In my main method  I create an instance of it and assign values to it   CIFSPacket packet   new CIFSPacket    packet protocolIdentifier   0xff  packet command    byte CommandTypes SMB COM NEGOTIATE  packet errorClass   0xff  packet error   0  packet flags   0x00  packet flags2   0x0001  packet multiplexId   22  packet wordCount   0  packet byteCount   119   packet Buffer    NT LM 0 12     Now I want to send this Packet by socket  For that  I need to convert the structure to a byte array  How can I do it   My full code is as follows   static void Main string   args       Socket MyPing   new Socket AddressFamily InterNetwork    SocketType Stream   ProtocolType Unspecified         MyPing Connect  172 24 18 240   139          Fake an IP Address so I can send with SendTo     IPAddress IP   new IPAddress new byte     172 24 18 240         IPEndPoint IPEP   new IPEndPoint IP  139          Local IP for Receiving     IPEndPoint Local   new IPEndPoint IPAddress Any  0       EndPoint EP    EndPoint Local       CIFSPacket packet   new CIFSPacket        packet protocolIdentifier   0xff      packet command    byte CommandTypes SMB COM NEGOTIATE      packet errorClass   0xff      packet error   0      packet flags   0x00      packet flags2   0x0001      packet multiplexId   22      packet wordCount   0      packet byteCount   119       packet Buffer    NT LM 0 12        MyPing SendTo It takes byte array as parameter       What would a code snippet be

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Abdel Olakara answer donese not work in  net 3 5  should be modified as below       public static void ByteArrayToStructure lt T gt  byte   bytearray  ref T obj                int len   Marshal SizeOf obj           IntPtr i   Marshal AllocHGlobal len           Marshal Copy bytearray  0  i  len           obj    T Marshal PtrToStructure i  typeof T            Marshal FreeHGlobal i

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As the main answer is using CIFSPacket type  which is not  or no longer  available in C   I wrote correct methods       static byte   getBytes object str                int size   Marshal SizeOf str           byte   arr   new byte size           IntPtr ptr   Marshal AllocHGlobal size            Marshal StructureToPtr str  ptr  true           Marshal Copy ptr  arr  0  size           Marshal FreeHGlobal ptr            return arr             static T fromBytes lt T gt  byte   arr                T str   default T            int size   Marshal SizeOf str           IntPtr ptr   Marshal AllocHGlobal size            Marshal Copy arr  0  ptr  size            str    T Marshal PtrToStructure ptr  str GetType             Marshal FreeHGlobal ptr            return str          Tested  they work

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Looks like a predefined  C level  structure for some external library  Marshal is your friend  Check   http   geekswithblogs net taylorrich archive 2006 08 21 88665 aspx  for a starter how to deal with this  Note that you can - with attributes - define things like byte layout and string handling  VERY nice approach  actually   Neither BinaryFormatter Nor MemoryStream are done for that

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This can be done very straightforwardly   Define your struct explicitly with  StructLayout LayoutKind Explicit    int size   list GetLength 0   IntPtr addr   Marshal AllocHGlobal size   sizeof DataStruct    DataStruct  ptrBuffer    DataStruct  addr  foreach  DataStruct ds in list         ptrBuffer   ds      ptrBuffer    1      This code can only be written in an unsafe context  You have to free addr when you re done with it   Marshal FreeHGlobal addr

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Header header   new Header            Byte   headerBytes   new Byte Marshal SizeOf header            Marshal Copy  IntPtr   amp header   headerBytes  0  headerBytes Length     This should do the trick quickly  right

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If you really want it to be FAST on Windows  you can do it using unsafe code with CopyMemory  CopyMemory is about 5x faster  e g  800MB of data takes 3s to copy via marshalling  while only taking  6s to copy via CopyMemory   This method does limit you to using only data which is actually stored in the struct blob itself  e g  numbers  or fixed length byte arrays        DllImport  kernel32 dll   EntryPoint    CopyMemory   SetLastError   false       private static unsafe extern void CopyMemory void  dest  void  src  int count        private static unsafe byte   Serialize TestStruct   index                var buffer   new byte Marshal SizeOf typeof TestStruct     index Length           fixed  void  d    amp buffer 0                         fixed  void  s    amp index 0                                 CopyMemory d  s  buffer Length                                    return buffer

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Have a look at these methods   byte    StructureToByteArray object obj        int len   Marshal SizeOf obj        byte    arr   new byte len        IntPtr ptr   Marshal AllocHGlobal len        Marshal StructureToPtr obj  ptr  true        Marshal Copy ptr  arr  0  len        Marshal FreeHGlobal ptr        return arr     void ByteArrayToStructure byte    bytearray  ref object obj        int len   Marshal SizeOf obj        IntPtr i   Marshal AllocHGlobal len        Marshal Copy bytearray 0  i len        obj   Marshal PtrToStructure i  obj GetType          Marshal FreeHGlobal i       This is a shameless copy of another thread which I found upon Googling   Update   For more details  check the source

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I know this is really late  but with C  7 3 you can do this for unmanaged structs or anything else that s unmanged  int  bool etc       public static unsafe byte   ConvertToBytes lt T gt  T value  where T   unmanaged           byte  pointer    byte   amp value           byte   bytes   new byte sizeof T            for  int i   0  i  lt  sizeof T   i                  bytes i    pointer i                      return bytes          Then use like this   struct MyStruct           public int Value1          public int Value2               blah blah blah            byte   bytes   ConvertToBytes new MyStruct

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You can use Marshal  StructureToPtr  ptrToStructure   and Marshal copy but this is plataform dependent     Serialization includes Functions to Custom Serialization   public virtual void GetObjectData SerializationInfo info  StreamingContext context  Protected Sub New ByVal info As SerializationInfo  ByVal context As StreamingContext     SerializationInfo include functions to serialize each member     BinaryWriter and BinaryReader also contains methods to Save   Load to Byte Array  Stream    Note that you can create a MemoryStream from a Byte Array or a Byte Array from a MemoryStream   You can create a method Save and a method New on your structure      Save Bw as BinaryWriter     New  Br as BinaryReader    Then you select members to Save   Load to Stream -  Byte Array

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This is fairly easy  using marshalling   Top of file  using System Runtime InteropServices   Function  byte   getBytes CIFSPacket str        int size   Marshal SizeOf str       byte   arr   new byte size        IntPtr ptr   Marshal AllocHGlobal size       Marshal StructureToPtr str  ptr  true       Marshal Copy ptr  arr  0  size       Marshal FreeHGlobal ptr       return arr      And to convert it back   CIFSPacket fromBytes byte   arr        CIFSPacket str   new CIFSPacket         int size   Marshal SizeOf str       IntPtr ptr   Marshal AllocHGlobal size        Marshal Copy arr  0  ptr  size        str    CIFSPacket Marshal PtrToStructure ptr  str GetType         Marshal FreeHGlobal ptr        return str      In your structure  you will need to put this before a string   MarshalAs UnmanagedType ByValTStr  SizeConst   100   public string Buffer    And make sure SizeConst is as big as your biggest possible string   And you should probably read this  http   msdn microsoft com en-us library 4ca6d5z7 aspx

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I ve come up with a different approach that could convert any struct without the hassle of fixing length  however the resulting byte array would have a little bit more overhead   Here is a sample struct    StructLayout LayoutKind Sequential   public class HelloWorld       public MyEnum enumvalue      public string reqtimestamp      public string resptimestamp      public string message      public byte   rawresp      As you can see  all those structures would require adding the fixed length attributes  Which could often ended up taking up more space than required  Note that the LayoutKind Sequential is required  as we want reflection to always gives us the same order when pulling for FieldInfo  My inspiration is from TLV Type-Length-Value  Let s have a look at the code   public static byte   StructToByteArray lt T gt  T obj        using  MemoryStream ms   new MemoryStream                  FieldInfo   infos   typeof T  GetFields BindingFlags Public   BindingFlags Instance           foreach  FieldInfo info in infos                        BinaryFormatter bf   new BinaryFormatter                using  MemoryStream inms   new MemoryStream                       bf Serialize inms  info GetValue obj                    byte   ba   inms ToArray                       for length                 ms Write BitConverter GetBytes ba Length   0  sizeof int                        for value                 ms Write ba  0  ba Length                                    return ms ToArray              The above function simply uses the BinaryFormatter to serialize the unknown size raw object  and I simply keep track of the size as well and store it inside the output MemoryStream too    public static void ByteArrayToStruct lt T gt  byte   data  out T output        output    T  Activator CreateInstance typeof T   null       using  MemoryStream ms   new MemoryStream data                 byte   ba   null          FieldInfo   infos   typeof T  GetFields BindingFlags Public   BindingFlags Instance           foreach  FieldInfo info in infos                           for length             ba   new byte sizeof int                ms Read ba  0  sizeof int                    for value             int sz   BitConverter ToInt32 ba  0               ba   new byte sz               ms Read ba  0  sz                BinaryFormatter bf   new BinaryFormatter                using  MemoryStream inms   new MemoryStream ba                                 info SetValue output  bf Deserialize inms                                      When we want to convert it back to its original struct we simply read the length back and directly dump it back into the BinaryFormatter which in turn dump it back into the struct   These 2 functions are generic and should work with any struct  I ve tested the above code in my C  project where I have a server and a client  connected and communicate via NamedPipeStream and I forward my struct as byte array from one and to another and converted it back   I believe my approach might be better  since it doesn t fix length on the struct itself and the only overhead is just an int for every fields you have in your struct  There are also some tiny bit overhead inside the byte array generated by BinaryFormatter  but other than that  is not much

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I would take a look at the BinaryReader and BinaryWriter classes  I recently had to serialize data to a byte array  and back  and only found these classes after I d basically rewritten them myself   http   msdn microsoft com en-us library system io binarywriter aspx  There is a good example on that page too

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Variant of the code of Vicent with one less memory allocation   public static byte   GetBytes lt T gt  T str        int size   Marshal SizeOf str        byte   arr   new byte size        GCHandle h   default GCHandle        try               h   GCHandle Alloc arr  GCHandleType Pinned            Marshal StructureToPtr lt T gt  str  h AddrOfPinnedObject    false             finally               if  h IsAllocated                        h Free                         return arr     public static T FromBytes lt T gt  byte   arr  where T   struct       T str   default T        GCHandle h   default GCHandle        try               h   GCHandle Alloc arr  GCHandleType Pinned            str   Marshal PtrToStructure lt T gt  h AddrOfPinnedObject                finally               if  h IsAllocated                        h Free                         return str      I use GCHandle to  pin  the memory and then I use directly its address with h AddrOfPinnedObject

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This example here is only applicable to pure blittable types  e g   types that can be memcpy d directly in C   Example - well known 64-bit struct   StructLayout LayoutKind Sequential     public struct Voxel       public ushort m id      public byte m red  m green  m blue  m alpha  m matid  m custom      Defined exactly like this  the struct will be automatically packed as 64-bit   Now we can create volume of voxels   Voxel     voxels   new Voxel 16 16 16     And save them all to a byte array   int size   voxels Length   8     Well known size  64 bits byte   saved   new byte size   GCHandle h   GCHandle Alloc voxels  GCHandleType Pinned   Marshal Copy h AddrOfPinnedObject    saved  0  size   h Free       now feel free to save  saved  to a File   memory stream    However  since the OP wants to know how to convert the struct itself  our Voxel struct can have following method ToBytes   byte   bytes   new byte 8      Well known size  64 bits GCHandle h   GCHandle Alloc this  GCHandleType Pinned   Marshal Copy hh AddrOfPinnedObject    bytes  0  8   h Free

[c#] How to convert a structure to a byte array in C#?

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