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Posted 11 Feb 2007
Licenced CPOL

Pinned Object

, 11 Feb 2007
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A helper class for working with structures that need to be pinned to prevent the GC from moving them.


This article describes a very short helper class to work with unmanaged memory that must be pinned to prevent the garbage collector from moving it. This is a particular requirement when working with the Win32 API's asynchronous I/O methods, which I found myself doing when implementing a USB device interface.

There is no download; simply copy the code from this article--please do not remove the copyright.

The Code

There really isn't much to this code:

  • It uses generics to internally cast the unmanaged memory to the desired managed type.
  • The class maintains an instance of the managed structure.
  • The constructor pins this structure and initializes a pointer suitable for working with Win32 API methods.
  • The ManagedObject property is used to return a managed object that references the unmanaged memory and to copy the managed object to the unmanaged memory. One caveat is that the managed object must be a structure suitable for use with the Marshal class.
  • The Pointer property is used to return the address of the unmanaged memory.
  • The destructor disposes of the unmanaged memory.
  • The class implements IDisposable, so that you can use this class in a "using" block as well.

Here's the code:

// (c) 2007 Marc Clifton
using System;
using System.Runtime.InteropServices;

namespace Clifton.Tools.Interop
  /// <summary>
  /// A helper class for pinning a managed structure so that it is suitable for
  /// unmanaged calls. A pinned object will not be collected and will not be moved
  /// by the GC until explicitly freed.
  /// </summary>
  public class PinnedObject<T> : IDisposable where T : struct
    protected T managedObject;
    protected GCHandle handle;
    protected IntPtr ptr;
    protected bool disposed;

    public T ManangedObject
        return (T)handle.Target;
        Marshal.StructureToPtr(value, ptr, false);

    public IntPtr Pointer
      get { return ptr; }

    public PinnedObject()
      handle = GCHandle.Alloc(managedObject, GCHandleType.Pinned);
      ptr = handle.AddrOfPinnedObject();


    public void Dispose()
      if (!disposed)
        ptr = IntPtr.Zero;
        disposed = true;


Using Unsafe Pointers In C#

This example illustrates manipulating a PinnedObject using C++ style pointer syntax within an unsafe code block. The code illustrates:

  • Assigning a new structure to the pinned object (testing the ManagedObject setter)
  • Getting the pointer and manipulating the structure via the pointer (testing the Pointer getter)
  • Getting the structure (testing the ManagedObject getter)
using System;

using Clifton.Tools.Interop;

namespace pintest
  public struct TestStruct
    public int a;

  public static class Test
    public static void Main()
      PinnedObject<TestStruct> pin = new PinnedObject<TestStruct>();
      TestStruct ts = new TestStruct();
      ts.a = 1;
      pin.ManangedObject = ts;

        TestStruct* p = (TestStruct*)pin.Pointer;



A simple class but hopefully you will find it useful for the strong type management and functionality that it encapsulates.


This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)


About the Author

Marc Clifton
Architect Interacx
United States United States
Home Page:

All my life I have been passionate about architecture / software design, as this is the cornerstone to a maintainable and extensible application. As such, I have enjoyed exploring some crazy ideas and discovering that they are not so crazy after all. I also love writing about my ideas and seeing the community response. As a consultant, I've enjoyed working in a wide range of industries such as aerospace, boatyard management, remote sensing, emergency services / data management, and casino operations. I've done a variety of pro-bono work non-profit organizations related to nature conservancy, drug recovery and women's health.

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Comments and Discussions

GeneralPinning copy of the structure Pin
Lesheniuk2-Mar-07 5:04
memberLesheniuk2-Mar-07 5:04 
GeneralRe: Pinning copy of the structure Pin
Marc Clifton2-Mar-07 5:18
protectorMarc Clifton2-Mar-07 5:18 
Questionfixed statement Pin
rvpilot13-Feb-07 10:48
memberrvpilot13-Feb-07 10:48 
AnswerRe: fixed statement Pin
Marc Clifton13-Feb-07 11:06
protectorMarc Clifton13-Feb-07 11:06 
GeneralRe: fixed statement Pin
rvpilot13-Feb-07 11:14
memberrvpilot13-Feb-07 11:14 
GeneralTesting Pin
Luc Pattyn12-Feb-07 12:07
professionalLuc Pattyn12-Feb-07 12:07 
GeneralRe: Testing Pin
Marc Clifton12-Feb-07 13:28
protectorMarc Clifton12-Feb-07 13:28 
GeneralMy .NET 1.1 approach, without generics Pin
Luc Pattyn12-Feb-07 11:27
professionalLuc Pattyn12-Feb-07 11:27 

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