StructLayoutAttribute Class
Updated: June 2011
The StructLayoutAttribute class allows the user to control the physical layout of the data fields of a class or structure.
Assembly: mscorlib (in mscorlib.dll)
You can apply this attribute to classes or structures.
The common language runtime controls the physical layout of the data fields of a class or structure in managed memory. However, if you want to pass the type to unmanaged code, you can use the StructLayoutAttribute attribute to control the unmanaged layout of the type. Use the attribute with LayoutKind.Sequential to force the members to be laid out sequentially in the order they appear. For blittable types, LayoutKind.Sequential controls both the layout in managed memory and the layout in unmanaged memory. For non-blittable types, it controls the layout when the class or structure is marshaled to unmanaged code, but does not control the layout in managed memory. Use the attribute with LayoutKind.Explicit to control the precise position of each data member. This affects both managed and unmanaged layout, for both blittable and non-blittable types. Using LayoutKind.Explicit requires that you use the FieldOffsetAttribute attribute to indicate the position of each field within the type.
C#, Visual Basic, and C++ compilers apply the Sequential layout value to structures by default. For classes, you must apply the LayoutKind.Sequential value explicitly. The Type Library Importer (Tlbimp.exe) also applies the StructLayoutAttribute attribute; it always applies the LayoutKind.Sequential value when it imports a type library.
The following example demonstrates a managed declaration of the GetSystemTime function and defines MySystemTime class with LayoutKind.Explicit layout. GetSystemTime gets the system time and prints to the console.
Imports System Imports System.Runtime.InteropServices Namespace InteropSample <StructLayout(LayoutKind.Explicit, Size:=16, CharSet:=CharSet.Ansi)> _ Public Class MySystemTime <FieldOffset(0)> Public wYear As Short <FieldOffset(2)> Public wMonth As Short <FieldOffset(4)> Public wDayOfWeek As Short <FieldOffset(6)> Public wDay As Short <FieldOffset(8)> Public wHour As Short <FieldOffset(10)> Public wMinute As Short <FieldOffset(12)> Public wSecond As Short <FieldOffset(14)> Public wMilliseconds As Short End Class 'MySystemTime Class LibWrapper <DllImport("kernel32.dll")> _ Public Shared Sub GetSystemTime(<MarshalAs(UnmanagedType.LPStruct)> ByVal st As MySystemTime) End Sub End Class 'LibWrapper Class TestApplication Public Shared Sub Main() Try Dim sysTime As New MySystemTime() LibWrapper.GetSystemTime(sysTime) Console.WriteLine("The System time is {0}/{1}/{2} {3}:{4}:{5}", sysTime.wDay, sysTime.wMonth, sysTime.wYear, sysTime.wHour, sysTime.wMinute, sysTime.wSecond) Catch e As TypeLoadException Console.WriteLine(("TypeLoadException : " + e.Message.ToString())) Catch e As Exception Console.WriteLine(("Exception : " + e.Message.ToString())) End Try End Sub 'Main End Class 'TestApplication End Namespace 'InteropSample
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The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.