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TypeBuilder::DefineUninitializedData Method

Defines an uninitialized data field in the .sdata section of the portable executable (PE) file.

Namespace:  System.Reflection.Emit
Assembly:  mscorlib (in mscorlib.dll)

FieldBuilder^ DefineUninitializedData(
	String^ name, 
	int size, 
	FieldAttributes attributes


Type: System::String
The name used to refer to the data. name cannot contain embedded nulls.
Type: System::Int32
The size of the data field.
Type: System.Reflection::FieldAttributes
The attributes for the field.

Return Value

Type: System.Reflection.Emit::FieldBuilder
A field to reference the data.


Length of name is zero.


size is less than or equal to zero, or greater than or equal to 0x003f0000.


name is nullptr.


The type was previously created using CreateType.

The field that you create with this method will be static, even if you do not include FieldAttributes.Static in the attributes parameter.

The following code sample demonstrates the use of DefineUninitializedData to create an uninitialized data field in a dynamic type:

using namespace System;
using namespace System::Threading;
using namespace System::Reflection;
using namespace System::Reflection::Emit;
using namespace System::Runtime::InteropServices;
using namespace System::Security::Permissions;

public ref class Example
   [SecurityPermission(SecurityAction::Demand, Flags=SecurityPermissionFlag::UnmanagedCode)]
   static void Main()
      Type^ myHelloWorldType = CreateCallee( Thread::GetDomain() );
      Object^ myHelloWorldInstance = Activator::CreateInstance( myHelloWorldType );
      FieldInfo^ myGreetingFieldInfo = myHelloWorldType->GetField( "MyGreeting" );
      Object^ oval = Activator::CreateInstance( myGreetingFieldInfo->FieldType );
      IntPtr myIntPtr = Marshal::AllocHGlobal( 4 );
      Random^ rand = gcnew Random;
      int iTempSeed = rand->Next();
      array<Byte>^bINITBYTE = GetRandBytes( iTempSeed, 4 );
      IntPtr intptrTemp = myIntPtr;
      for ( int j = 0; j < 4; j++ )
         Marshal::WriteByte( myIntPtr, bINITBYTE[ j ] );
         myIntPtr = (IntPtr)((int)myIntPtr + 1);

      myIntPtr = intptrTemp;
      Object^ oValNew = Marshal::PtrToStructure( myIntPtr, myGreetingFieldInfo->FieldType );
      Marshal::FreeHGlobal( myIntPtr );
      myIntPtr = Marshal::AllocHGlobal( 4 );
      Object^ myObj = myGreetingFieldInfo->GetValue( myHelloWorldInstance );
      Marshal::StructureToPtr( myObj, myIntPtr, true );
      intptrTemp = myIntPtr;
      Console::WriteLine( "The value of 'MyGreeting' field : " );
      for ( int j = 0; j < 4; j++ )
         Marshal::WriteByte( myIntPtr, bINITBYTE[ j ] );
         Console::WriteLine( bINITBYTE[ j ] );
         myIntPtr = (IntPtr)((int)myIntPtr + 1);


   static array<Byte>^ GetRandBytes( int iRandSeed, int iSize )
      array<Byte>^barr = gcnew array<Byte>(iSize);
      Random^ randTemp = gcnew Random( iRandSeed );
      randTemp->NextBytes( barr );
      return barr;

   // Create the callee transient dynamic assembly.
   static Type^ CreateCallee( AppDomain^ myDomain )

      // Create a simple name for the callee assembly.
      AssemblyName^ myAssemblyName = gcnew AssemblyName;
      myAssemblyName->Name = "EmittedClass";

      // Create the callee dynamic assembly.
      AssemblyBuilder^ myAssembly = myDomain->DefineDynamicAssembly( myAssemblyName, AssemblyBuilderAccess::Run );

      // Create a dynamic module in the callee assembly.
      ModuleBuilder^ myModule = myAssembly->DefineDynamicModule( "EmittedModule" );

      // Define a public class named "MyHelloWorld"
      TypeBuilder^ myHelloWorldType = myModule->DefineType( "MyHelloWorld", TypeAttributes::Public );

      // Define a 'MyGreeting' field and initialize it.
      FieldBuilder^ myFieldBuilder = myHelloWorldType->DefineUninitializedData( "MyGreeting", 4, FieldAttributes::Public );

      // Create the 'MyHelloWorld' class.
      return (myHelloWorldType->CreateType());


int main()

.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

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.