C# - struct serialization

Question

I have got a small class that I would like to use for serializing structs. I would like to know two things:

• Performance issue. Since I am passing Object - it passes just a reference, not a copy of the struct? And since I am returning object of type T it also only passes a reference?

• Correctness issue. Will this serialization work for all structs? I mean - is there a possibility where those methods will not work?

  public static byte[] ToByteArray(Object obj)
  {
      int size = Marshal.SizeOf(obj);
      byte[] arr = new byte[size];
      IntPtr ptr = Marshal.AllocHGlobal(size);
  
      Marshal.StructureToPtr(obj, ptr, true);
      Marshal.Copy(ptr, arr, 0, size);
      Marshal.FreeHGlobal(ptr);
  
      return arr;
  }
  
  public static T ToStructure<T>(byte[] arr) where T : new()
  {
      T str = new 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;
  }        
  

Thanks, guys!

EDIT

I now specify that these are structs. Nothing is being copied now?

    public static byte[] ToByteArray<T>(ref T str) where T : struct
    {
        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;
    }

    public static T ToStructure<T>(byte[] arr) where T : struct
    {
        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;
    }

Answer 1

1. It WILL copy. This is called "boxing". The only way to pass a reference to a struct S is to have a parameter declared as ref S.
2. It wont handled nested stuff such as members that are array, string or any class type.

FYI With generics you can constrain a method to just apply to structs with "where T:struct"

Answer 2

1. This will not serialize references correctly (i.e. any field of a non-primitive and non-struct type).
2. It doesn't include type data
   • Which makes it unsuitable for cases when not all types are known beforehand or some types have changed slightly since serialization time.
3. (Minor) ToStructure doesn't validate the binary data

Why not learn about the existing solutions before reinventing the wheel? The Serialization Guidelines article says there are 3 serialization techniques implemented in the .NET framework that have different characteristics and are tailored for different purposes.

Here's an example of the simplest, 3rd technique given as example in the Object Serialization in .NET article. It exists to reconstruct an object with exactly the same type and internal data as the original one (which means, serialization includes the objects it references).
_{(the code is in IronPython yet I hope it's readable enough to understand what's going on)}

>>> l=System.Collections.Generic.List[System.Drawing.Point]\
([System.Drawing.Point(*(random.randint(1,1000) for _ in range(2))) for _ in range(5)])
>>> l
List[Point]([<System.Drawing.Point object at 0x0000000000000233 [{X=491,Y=874}]>
, <System.Drawing.Point object at 0x0000000000000234 [{X=819,Y=595}]>, <System.D
rawing.Point object at 0x0000000000000235 [{X=456,Y=625}]>, <System.Drawing.Poin
t object at 0x0000000000000236 [{X=583,Y=29}]>, <System.Drawing.Point object at
0x0000000000000237 [{X=329,Y=212}]>])
>>> szr=System.Runtime.Serialization.Formatters.Binary.BinaryFormatter()
>>> stm=System.IO.MemoryStream()
>>> szr.Serialize(stm,l)
>>> stm.Length
481L
>>> bytes=stm.GetBuffer()
>>> s=''.join(chr(b) for b in bytes)
>>> s
u'\x00\x01\x00\x00\x00\xff\xff\xff\xff\x01\x00\x00\x00\x00\x00\x00\x00\x0c\x02\x
00\x00\x00QSystem.Drawing, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f
5f7f11d50a3a\x04\x01\x00\x00\x00\x8c\x01System.Collections.Generic.List`1[[Syste
m.Drawing.Point, System.Drawing, Version=4.0.0.0, Culture=neutral, PublicKeyToke
n=b03f5f7f11d50a3a]]\x03\x00\x00\x00\x06_items\x05_size\x08_version\x04\x00\x00\
x16System.Drawing.Point[]\x02\x00\x00\x00\x08\x08\t\x03\x00\x00\x00\x05\x00\x00\
x00\x00\x00\x00\x00\x07\x03\x00\x00\x00\x00\x01\x00\x00\x00\x05\x00\x00\x00\x04\
x14System.Drawing.Point\x02\x00\x00\x00\x05\xfc\xff\xff\xff\x14System.Drawing.Po
int\x02\x00\x00\x00\x01x\x01y\x00\x00\x08\x08\x02\x00\x00\x00\xeb\x01\x00\x00j\x
03\x00\x00\x01\xfb\xff\xff\xff\xfc\xff\xff\xff3\x03\x00\x00S\x02\x00\x00\x01\xfa
\xff\xff\xff\xfc\xff\xff\xff\xc8\x01\x00\x00q\x02\x00\x00\x01\xf9\xff\xff\xff\xf
c\xff\xff\xffG\x02\x00\x00\x1d\x00\x00\x00\x01\xf8\xff\xff\xff\xfc\xff\xff\xffI\
x01\x00\x00\xd4\x00\x00\x00\x0b\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\
x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00'