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IntPtr.Zero Field

A read-only field that represents a pointer or handle that has been initialized to zero.

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

public static readonly IntPtr Zero

The value of this field is not equivalent to null. Use this field to efficiently determine whether an instance of IntPtr has been set to a value other than zero.

For example, assume the variable, ip, is an instance of IntPtr. You can determine if it has been set by comparing it to the value returned by a constructor, for example: " if ip != new IntPtr(0)... ". However, invoking a constructor to get an unintialized pointer is inefficient. It is better to code either " if ip != IntPtr.Zero... ", or " if !IntPtr.Zero.Equals(ip)... ".

When calling the Windows API from managed code, you can pass IntPtr.Zero instead of null if an argument is expected to be either a pointer or a null. For example, the following call to the Windows CreateFile function supplies IntPtr.Zero for the pSecurityAttributes and hTemplateFile argument values.

using Microsoft.Win32.SafeHandles;
using System;
using System.Runtime.InteropServices;

public class Example
{
   private const uint GENERIC_READ = 0x80000000;
   private const uint OPEN_EXISTING = 3; 
   private const uint FILE_ATTRIBUTE_NORMAL = 128;
   private const uint FILE_FLAG_OVERLAPPED = 0x40000000;

   [DllImport("kernel32.dll", SetLastError = true, CharSet = CharSet.Unicode)]
   private static extern Microsoft.Win32.SafeHandles.SafeFileHandle CreateFile(
            string lpFileName, System.UInt32 dwDesiredAccess, System.UInt32 dwShareMode, 
            IntPtr pSecurityAttributes, System.UInt32 dwCreationDisposition, 
            System.UInt32 dwFlagsAndAttributes, IntPtr hTemplateFile);

   public static void Main()
   {
      SafeFileHandle hnd = CreateFile("CallOfTheWild.txt", GENERIC_READ, 0, 
                                      IntPtr.Zero, OPEN_EXISTING,
                                      FILE_ATTRIBUTE_NORMAL | FILE_FLAG_OVERLAPPED, 
                                      IntPtr.Zero);
      if (hnd.IsInvalid) {
            Exception ex = Marshal.GetExceptionForHR(Marshal.GetHRForLastWin32Error());
            Console.WriteLine("Attempt to open file failed:");
            Console.WriteLine("  {0}", ex.Message);
            return;           
      }                        
      else {
         Console.WriteLine("File successfully opened.");
         hnd.Close();     
      }
   }
}
// If the file cannot be found, the example displays the following output: 
//    Attempt to open file failed: 
//      The system cannot find the file specified. (Exception from HRESULT: 0x80070002)
NoteNote

Although Zero is equivalent to null for Windows API functions with parameters or return values that can be either pointers or null, Zero is not equivalent to null. Passing null to the IntPtr.Zero.Equals method always returns false.

You can also test for a null return value from Windows API function calls that return either a pointer or a null by comparing the returned value with IntPtr.Zero. For example, the call to the GetWindow function in the following example tries to retrieve the handle of a non-existent window. If it were called from unmanaged code, the function would return null, but when it is called from managed code, it returns IntPtr.Zero.

using System;
using System.Runtime.InteropServices;

public class Example
{
   private const int GW_OWNER = 4;

   [DllImport("user32", CharSet=CharSet.Auto, SetLastError=true, ExactSpelling=true)]
   public static extern IntPtr GetWindow(IntPtr hwnd, int wFlag);   

   public static void Main()
   {
      IntPtr hwnd = new IntPtr(3);
      IntPtr hOwner = GetWindow(hwnd, GW_OWNER);
      if (hOwner == IntPtr.Zero)
         Console.WriteLine("Window not found.");
   }
}
// The example displays the following output: 
//        Window not found.

.NET Framework

Supported in: 4.5.2, 4.5.1, 4.5, 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

.NET for Windows Store apps

Supported in: Windows 8

.NET for Windows Phone apps

Supported in: Windows Phone 8.1, Windows Phone 8, Silverlight 8.1

Windows Phone 8.1, Windows Phone 8, Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

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

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