LayoutKind LayoutKind LayoutKind LayoutKind Enum


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

public enum class LayoutKind
public enum LayoutKind
type LayoutKind = 
Public Enum LayoutKind


Auto Auto Auto Auto 3

The 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.

Explicit Explicit Explicit Explicit 2

The precise position of each member of an object in unmanaged memory is explicitly controlled, subject to the setting of the Pack field. Each member must use the FieldOffsetAttribute to indicate the position of that field within the type.

Sequential Sequential Sequential Sequential 0

The 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 Pack, and can be noncontiguous.


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 class Bool
   False = 0,

value struct Point
   int x;
   int y;

value struct Rect

   int left;

   int top;

   int right;

   int bottom;

ref class NativeMethods

   static Bool PtInRect( Rect * r, Point p );

int main()
      Bool bPointInRect = (Bool)0;
      Rect myRect = Rect(  );
      myRect.left = 10;
      myRect.right = 100; = 10;
      myRect.bottom = 100;
      Point myPoint = Point(  );
      myPoint.x = 50;
      myPoint.y = 50;
      bPointInRect = NativeMethods::PtInRect(  &myRect, myPoint );
      if ( bPointInRect == Bool::True )
            Console::WriteLine( "Point lies within the Rect" );
            Console::WriteLine( "Point did not lie within the Rect" );
   catch ( Exception^ e ) 
      Console::WriteLine( "Exception : {0}", e->Message );


enum Bool
   False = 0,
public struct Point 
   public int x;
   public int y;

public struct Rect 
   [FieldOffset(0)] public int left;
   [FieldOffset(4)] public int top;
   [FieldOffset(8)] public int right;
   [FieldOffset(12)] public int bottom;

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

class TestApplication
   public static void Main()
         Bool bPointInRect = 0;
         Rect myRect = new Rect();
         myRect.left = 10;
         myRect.right = 100; = 10;
         myRect.bottom = 100;
         Point myPoint = new Point();
         myPoint.x = 50;
         myPoint.y = 50;
         bPointInRect = NativeMethods.PtInRect(ref myRect, myPoint);
         if(bPointInRect == Bool.True)
            Console.WriteLine("Point lies within the Rect");
            Console.WriteLine("Point did not lie within the Rect");
      catch(Exception e)
         Console.WriteLine("Exception : " + e.Message);
'  The program shows a managed declaration of the PtInRect function and defines Point
'  structure with sequential layout and Rect structure with explicit layout. The PtInRect
'  checks the point lies within the rectangle or not.
Imports System
Imports System.Runtime.InteropServices

   Enum Bool
      [False] = 0
   End Enum 
   <StructLayout(LayoutKind.Sequential)>  _
   Public Structure Point
      Public x As Integer
      Public y As Integer
   End Structure 
   <StructLayout(LayoutKind.Explicit)>  _   
   Public Structure Rect
      <FieldOffset(0)> Public left As Integer
      <FieldOffset(4)> Public top As Integer
      <FieldOffset(8)> Public right As Integer
      <FieldOffset(12)> Public bottom As Integer
   End Structure 
   Friend Class NativeMethods
      <DllImport("user32.dll", CallingConvention := CallingConvention.StdCall)>  _
      Friend Shared Function PtInRect(ByRef r As Rect, p As Point) As Bool
      End Function	
   End Class 'NativeMethods
   Class TestApplication
      Public Shared Sub Main()
            Dim bPointInRect As Bool = 0
            Dim myRect As New Rect()
            myRect.left = 10
            myRect.right = 100
   = 10
            myRect.bottom = 100
            Dim myPoint As New Point()
            myPoint.x = 50
            myPoint.y = 50
            bPointInRect = NativeMethods.PtInRect(myRect, myPoint)
            If bPointInRect = Bool.True Then
               Console.WriteLine("Point lies within the Rect")
               Console.WriteLine("Point did not lie within the Rect")
            End If
         Catch e As Exception
            Console.WriteLine(("Exception : " + e.Message.ToString()))
         End Try
      End Sub 
   End Class 


This enumeration is used with StructLayoutAttribute. 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.


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.

Applies to