How to convert an object to a byte array in C

Question

I have a collection of objects that I need to write to a binary file     I need the bytes in the file to be compact  so I can t use BinaryFormatter   BinaryFormatter throws in all sorts of info for deserialization needs   If I try   byte   myBytes    byte    myObject    I get a runtime exception   I need this to be fast so I d rather not be copying arrays of bytes around   I d just like the cast byte   myBytes    byte    myObject to work    OK just to be clear  I cannot have any metadata in the output file   Just the object bytes   Packed object-to-object   Based on answers received  it looks like I ll be writing low-level Buffer BlockCopy code   Perhaps using unsafe code

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Well a cast from myObject to byte   is never going to work unless you ve got an explicit conversion or if myObject is a byte    You need a serialization framework of some kind  There are plenty out there  including Protocol Buffers which is near and dear to me  It s pretty  lean and mean  in terms of both space and time   You ll find that almost all serialization frameworks have significant restrictions on what you can serialize  however - Protocol Buffers more than some  due to being cross-platform   If you can give more requirements  we can help you out more - but it s never going to be as simple as casting     EDIT  Just to respond to this      I need my binary file to contain the   object s bytes  Only the bytes  no   metadata whatsoever  Packed   object-to-object  So I ll be   implementing custom serialization    Please bear in mind that the bytes in your objects are quite often references    so you ll need to work out what to do with them   I suspect you ll find that designing and implementing your own custom serialization framework is harder than you imagine   I would personally recommend that if you only need to do this for a few specific types  you don t bother trying to come up with a general serialization framework  Just implement an instance method and a static method in all the types you need   public void WriteTo Stream stream  public static WhateverType ReadFrom Stream stream    One thing to bear in mind  everything becomes more tricky if you ve got inheritance involved  Without inheritance  if you know what type you re starting with  you don t need to include any type information  Of course  there s also the matter of versioning - do you need to worry about backward and forward compatibility with different versions of your types

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You are really talking about serialization  which can take many forms  Since you want small and binary  protocol buffers may be a viable option - giving version tolerance and portability as well  Unlike BinaryFormatter  the protocol buffers wire format doesn t include all the type metadata  just very terse markers to identify data   In  NET there are a few implementations  in particular   protobuf-net dotnet-protobufs   I d humbly argue that protobuf-net  which I wrote  allows more  NET-idiomatic usage with typical C  classes   regular  protocol-buffers tends to demand code-generation   for example    ProtoContract  public class Person       ProtoMember 1      public int Id  get set       ProtoMember 2      public string Name  get set          Person person   new Person   Id   123  Name    abc     Serializer Serialize destStream  person       Person anotherPerson   Serializer Deserialize lt Person gt  sourceStream

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I believe what you re trying to do is impossible   The junk that BinaryFormatter creates is necessary to recover the object from the file after your program stopped  However it is possible to get the object data  you just need to know the exact size of it  more difficult than it sounds     public static unsafe byte   Binarize object obj  int size        var r   new byte size       var rf     makeref obj       var a      IntPtr     amp rf       Marshal Copy a  r  0  size       return res      this can be recovered via   public unsafe static dynamic ToObject byte   bytes        var rf     makeref bytes          int     amp rf     8      return GCHandle Alloc bytes  Target      The reason why the above methods don t work for serialization is that the first four bytes in the returned data correspond to a RuntimeTypeHandle  The RuntimeTypeHandle describes the layout type of the object but the value of it changes every time the program is ran   EDIT  that is stupid don t do that --  If you already know the type of the object to be deserialized for certain you can switch those bytes for BitConvertes GetBytes  int typeof yourtype  TypeHandle Value  at the time of deserialization

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This worked for me   byte   bfoo    byte   foo    foo is an Object that I m 100  certain that is a byte array

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To convert an object to a byte array      Convert an object to a byte array public static byte   ObjectToByteArray Object obj        BinaryFormatter bf   new BinaryFormatter        using  var ms   new MemoryStream                  bf Serialize ms  obj           return ms ToArray              You just need copy this function to your code and send to it the object that you need to convert to a byte array  If you need convert the byte array to an object again you can use the function below      Convert a byte array to an Object public static Object ByteArrayToObject byte   arrBytes        using  var memStream   new MemoryStream                  var binForm   new BinaryFormatter            memStream Write arrBytes  0  arrBytes Length           memStream Seek 0  SeekOrigin Begin           var obj   binForm Deserialize memStream           return obj            You can use these functions with custom classes  You just need add the  Serializable  attribute in your class to enable serialization

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Take a look at Serialization  a technique to  convert  an entire object to a byte stream  You may send it to the network or write it into a file and then restore it back to an object later

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If you want the serialized data to be really compact  you can write serialization methods yourself  That way you will have a minimum of overhead   Example   public class MyClass       public int Id   get  set       public string Name   get  set        public byte   Serialize           using  MemoryStream m   new MemoryStream               using  BinaryWriter writer   new BinaryWriter m                 writer Write Id               writer Write Name                       return m ToArray                     public static MyClass Desserialize byte   data          MyClass result   new MyClass          using  MemoryStream m   new MemoryStream data              using  BinaryReader reader   new BinaryReader m                 result Id   reader ReadInt32                result Name   reader ReadString                             return result

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I took Crystalonics  answer and turned them into extension methods   I hope someone else will find them useful   public static byte   SerializeToByteArray this object obj        if  obj    null                return null            var bf   new BinaryFormatter        using  var ms   new MemoryStream                  bf Serialize ms  obj           return ms ToArray             public static T Deserialize lt T gt  this byte   byteArray  where T   class       if  byteArray    null                return null            using  var memStream   new MemoryStream                  var binForm   new BinaryFormatter            memStream Write byteArray  0  byteArray Length           memStream Seek 0  SeekOrigin Begin           var obj    T binForm Deserialize memStream           return obj

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To access the memory of an object directly  to do a  core dump   you ll need to head into unsafe code   If you want something more compact than BinaryWriter or a raw memory dump will give you  then you need to write some custom serialisation code that extracts the critical information from the object and packs it in an optimal way   edit P S  It s very easy to wrap the BinaryWriter approach into a DeflateStream to compress the data  which will usually roughly halve the size of the data

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I found another way to convert an object to a byte    here is my solution  IEnumerable en    IEnumerable  myObject  byte   myBytes   en OfType lt byte gt    ToArray     Regards

[c#] How to convert an object to a byte array in C#

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