Question

What would be the best way to fill a C# struct from a byte[] array where the data was from a C/C++ struct? The C struct would look something like this (my C is very rusty):

typedef OldStuff {     CHAR Name[8];     UInt32 User;     CHAR Location[8];     UInt32 TimeStamp;     UInt32 Sequence;     CHAR Tracking[16];     CHAR Filler[12]; } 

And would fill something like this:

[StructLayout(LayoutKind.Explicit, Size = 56, Pack = 1)] public struct NewStuff {     [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 8)]     [FieldOffset(0)]     public string Name;      [MarshalAs(UnmanagedType.U4)]     [FieldOffset(8)]     public uint User;      [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 8)]     [FieldOffset(12)]     public string Location;      [MarshalAs(UnmanagedType.U4)]     [FieldOffset(20)]     public uint TimeStamp;      [MarshalAs(UnmanagedType.U4)]     [FieldOffset(24)]     public uint Sequence;      [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 16)]     [FieldOffset(28)]     public string Tracking; } 

What is best way to copy OldStuff to NewStuff, if OldStuff was passed as byte[] array?

I’m currently doing something like the following, but it feels kind of clunky.

GCHandle handle; NewStuff MyStuff;  int BufferSize = Marshal.SizeOf(typeof(NewStuff)); byte[] buff = new byte[BufferSize];  Array.Copy(SomeByteArray, 0, buff, 0, BufferSize);  handle = GCHandle.Alloc(buff, GCHandleType.Pinned);  MyStuff = (NewStuff)Marshal.PtrToStructure(handle.AddrOfPinnedObject(), typeof(NewStuff));  handle.Free(); 

Is there better way to accomplish this?

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Would using the BinaryReader class offer any performance gains over pinning the memory and using Marshal.PtrStructure?

Answer 1

From what I can see in that context, you don’t need to copy SomeByteArray into a buffer. You simply need to get the handle from SomeByteArray, pin it, copy the IntPtr data using PtrToStructure and then release. No need for a copy.

That would be:

NewStuff ByteArrayToNewStuff(byte[] bytes) {     GCHandle handle = GCHandle.Alloc(bytes, GCHandleType.Pinned);     try     {         NewStuff stuff = (NewStuff)Marshal.PtrToStructure(handle.AddrOfPinnedObject(), typeof(NewStuff));     }     finally     {         handle.Free();     }     return stuff; } 

Generic version:

T ByteArrayToStructure<T>(byte[] bytes) where T: struct  {     T stuff;     GCHandle handle = GCHandle.Alloc(bytes, GCHandleType.Pinned);     try     {         stuff = (T)Marshal.PtrToStructure(handle.AddrOfPinnedObject(), typeof(T));     }     finally     {         handle.Free();     }     return stuff; } 

Simpler version (requires unsafe switch):

unsafe T ByteArrayToStructure<T>(byte[] bytes) where T : struct {     fixed (byte* ptr = &bytes[0])     {         return (T)Marshal.PtrToStructure((IntPtr)ptr, typeof(T));     } }