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LayoutKind Enumeration

Updated: October 2011

Controls the layout of an object when it is exported to unmanaged code.

Namespace:  System.Runtime.InteropServices
Assembly:  mscorlib (in mscorlib.dll)

[SerializableAttribute]
[ComVisibleAttribute(true)]
public enum LayoutKind

Member nameDescription
Supported by the XNA FrameworkSupported by Portable Class LibrarySequentialThe members of the object are laid out sequentially, in the order in which they appear when exported to unmanaged memory. The members are laid out according to the packing specified in StructLayoutAttribute.Pack, and can be noncontiguous.
Supported by the XNA FrameworkSupported by Portable Class LibraryExplicitThe precise position of each member of an object in unmanaged memory is explicitly controlled, subject to the setting of the StructLayoutAttribute.Pack field. Each member must use the FieldOffsetAttribute attribute to indicate the position of that field within the type.
Supported by the XNA FrameworkSupported by Portable Class LibraryAutoThe runtime automatically chooses an appropriate layout for the members of an object in unmanaged memory. Objects defined with this enumeration member cannot be exposed outside of managed code. Attempting to do so generates an exception.

This enumeration is used with the StructLayoutAttribute attribute. The common language runtime uses the Auto layout value by default. To reduce layout-related problems associated with the Auto value, C#, Visual Basic, and C++ compilers specify Sequential layout for value types.

Important noteImportant

The StructLayoutAttribute.Pack field controls the alignment of data fields, and thus affects the layout regardless of the LayoutKind value you specify. By default, the value of Pack is 0, which indicates the default packing size for the current platform. For example, when you use the Explicit layout value and specify field alignments on byte boundaries, you must set Pack to 1 to get the desired result.

The following example shows the managed declaration of the PtInRect function, which checks whether a point lies within a rectangle, and defines a Point structure with Sequential layout and a Rect structure with Explicit layout.


enum Bool
{
   False = 0,
   True
};
[StructLayout(LayoutKind.Sequential)]
public struct Point 
{
   public int x;
   public int y;
}   

[StructLayout(LayoutKind.Explicit)]
public struct Rect 
{
   [FieldOffset(0)] public int left;
   [FieldOffset(4)] public int top;
   [FieldOffset(8)] public int right;
   [FieldOffset(12)] public int bottom;
}   

class LibWrapper
{
   [DllImport("user32.dll", CallingConvention=CallingConvention.StdCall)]
   public static extern Bool PtInRect(ref Rect r, Point p);
};

class TestApplication
{
   public static void Main()
   {
      try
      {
         Bool bPointInRect = 0;
         Rect myRect = new Rect();
         myRect.left = 10;
         myRect.right = 100;
         myRect.top = 10;
         myRect.bottom = 100;
         Point myPoint = new Point();
         myPoint.x = 50;
         myPoint.y = 50;
         bPointInRect = LibWrapper.PtInRect(ref myRect, myPoint);
         if(bPointInRect == Bool.True)
            Console.WriteLine("Point lies within the Rect");
         else
            Console.WriteLine("Point did not lie within the Rect");
      }
      catch(Exception e)
      {
         Console.WriteLine("Exception : " + e.Message);
      }
   }
}


.NET Framework

Supported in: 4, 3.5, 3.0, 2.0, 1.1, 1.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Portable Class Library

Supported in: Portable Class Library

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

Date

History

Reason

October 2011

Clarified that the StructLayoutAttribute.Pack field affects all values of LayoutKind.

Customer feedback.

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