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  1. using System;
  2. using System.Diagnostics;
  3. using System.Runtime.InteropServices;
  4. using System.Text;
  5.  
  6. public class Test
  7. {
  8. 	[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi, Size = 24)]
  9.     struct Valid
  10.     {
  11.         public uint Length;
  12.         public uint Version;
  13.         [MarshalAs(UnmanagedType.ByValArray, SizeConst = 16)]
  14.         public byte[] MachineId;
  15.     }
  16.  
  17.     [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi, Size = 24)]
  18.     struct Invalid
  19.     {
  20.         public uint Length;
  21.         public uint Version;
  22.         [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 16)] public string MachineId;
  23.     }
  24.  
  25. 	public static void Main()
  26. 	{
  27. 		var bytes = new byte[]
  28.         {
  29.             0x58, 0, 0, 0,
  30.             0, 0, 0, 0,
  31.             0x41, 0x42, 0x43, 0x44, 0x45, 0x46, 0x47, 0x48, 0x49, 0x4A, 0x4B, 0x4C, 0x4D, 0x4E, 0x4F, 0
  32.         };
  33.  
  34.         var pinnedBuffer = GCHandle.Alloc(bytes, GCHandleType.Pinned);
  35.         var ptr = pinnedBuffer.AddrOfPinnedObject();
  36.  
  37.         // Works!
  38.         Debug.Assert(bytes.Length == Marshal.SizeOf<Valid>());
  39.  
  40.         var trackerData1 = Marshal.PtrToStructure<Valid>(ptr);
  41.  
  42.         Console.WriteLine("Length: {0}", trackerData1.Length);
  43.         Console.WriteLine("Version: {0}", trackerData1.Version);
  44.         Console.WriteLine("MachineId: {0}", Encoding.ASCII.GetString(trackerData1.MachineId));
  45.  
  46.         // Doesnt work!
  47.         Debug.Assert(bytes.Length == Marshal.SizeOf<Invalid>());
  48.  
  49.         // Throws System.AccessViolationException
  50.         var trackerData2 = Marshal.PtrToStructure<Invalid>(ptr);
  51.  
  52.         Console.WriteLine("Length: {0}", trackerData2.Length);
  53.         Console.WriteLine("Version: {0}", trackerData2.Version);
  54.         Console.WriteLine("MachineId: {0}", trackerData2.MachineId);
  55.  
  56.         pinnedBuffer.Free();
  57.  
  58.         Console.In.ReadLine();
  59. 	}
  60. }
Success #stdin #stdout 0.01s 29664KB
comments (?)
stdin
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Standard input is empty
stdout
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Length: 88
Version: 0
MachineId: ABCDEFGHIJKLMNO
Length: 88
Version: 0
MachineId: ABCDEFGHIJKLMNO
https://ideone.com/J0bHhC
language:
C# (gmcs 5.20.1)
created:
8 years ago
visibility:
public

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