IntPtr.Zero IntPtr.Zero IntPtr.Zero IntPtr.Zero Field

Définition

Champ en lecture seule qui représente un pointeur ou un handle remis à zéro.A read-only field that represents a pointer or handle that has been initialized to zero.

public: static initonly IntPtr Zero;
public static readonly IntPtr Zero;
 staticval mutable Zero : nativeint
Public Shared ReadOnly Zero As IntPtr 

Valeur de champ

Remarques

La valeur de ce champ n’est pas équivalente à null.The value of this field is not equivalent to null. Utilisez ce champ pour déterminer efficacement si une instance de IntPtr a été définie sur une valeur autre que zéro.Use this field to efficiently determine whether an instance of IntPtr has been set to a value other than zero.

Par exemple, supposons que la variable IP est une instance de IntPtr.For example, assume the variable, ip, is an instance of IntPtr. Vous pouvez déterminer s’il a été défini en le comparant à la valeur retournée par un constructeur, par exemple if ip != new IntPtr(0)... : "".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)... ". Toutefois, l’appel d’un constructeur pour obtenir un pointeur non initialisé est inefficace.However, invoking a constructor to get an uninitialized pointer is inefficient. Il est préférable de coder soit « if ip != IntPtr.Zero... », if !IntPtr.Zero.Equals(ip)... soit «».It is better to code either " if ip != IntPtr.Zero... ", or " if !IntPtr.Zero.Equals(ip)... ".

Lors de l’appel de l’API Windows à partir du code IntPtr.Zero managé, null vous pouvez passer au lieu de si un argument est supposé être nullun pointeur ou un.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. Par exemple, l’appel suivant à la fonction CreateFile Windows fournit IntPtr.Zero les pSecurityAttributes valeurs d' hTemplateFile argument et.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)
Imports Microsoft.Win32.SafeHandles
Imports System
Imports System.Runtime.InteropServices

Module Example
   Private Const GENERIC_READ As UInteger = 2147483648
   Private Const OPEN_EXISTING As UInteger = 3 
   Private Const FILE_ATTRIBUTE_NORMAL As UInteger = 128
   Private Const FILE_FLAG_OVERLAPPED As UInteger = &h40000000

   Private Declare Auto Function CreateFile Lib "Kernel32" Alias "CreateFileW" (
            lpFileName As String, dwDesiredAccess As UInt32, 
            dwShareMode As UInt32, pSecurityAttributes As IntPtr, 
            dwCreationDisposition As UInt32, dwFlagsAndAttributes As UInt32, 
            hTemplateFile As IntPtr) As SafeFileHandle

   Public Sub Main()
      Dim hnd As SafeFileHandle = CreateFile("CallOfTheWild.txt", GENERIC_READ, 0, 
                                             IntPtr.Zero, OPEN_EXISTING,
                                             FILE_ATTRIBUTE_NORMAL Or FILE_FLAG_OVERLAPPED, 
                                             IntPtr.Zero)
      If hnd.IsInvalid Then
         Dim ex As Exception = 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()     
      End If
   End Sub
End Module
' 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)

Notes

Bien Zero que soit équivalent null à pour les fonctions API Windows avec des paramètres ou des valeurs de retour qui peuvent nullêtre Zero des pointeurs ou null, n’est pas équivalent à.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. Le null passage à IntPtr.Zero.Equals la méthode retourne falsetoujours.Passing null to the IntPtr.Zero.Equals method always returns false.

Vous pouvez également tester une null valeur de retour à partir des appels de fonctions API Windows qui retournent un pointeur ou un null en comparant la valeur retournée à IntPtr.Zero.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. Par exemple, l’appel à la GetWindow fonction dans l’exemple suivant tente de récupérer le handle d’une fenêtre inexistante.For example, the call to the GetWindow function in the following example tries to retrieve the handle of a non-existent window. S’il a été appelé à partir de code non managé, la fonction nullretourne, mais quand elle est appelée à partir du code managé IntPtr.Zero, elle retourne.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.
Module Example
   Private Const GW_OWNER As Integer = 4

   Private Declare Function GetWindow Lib "user32" (hWnd As IntPtr, 
                            wFlag As Integer) As IntPtr 

   Public Sub Main()
      Dim hwnd = new IntPtr(3)
      Dim hOwner As IntPtr = GetWindow(hwnd, GW_OWNER)
      If hOwner = IntPtr.Zero Then
         Console.WriteLine("Window not found.")
      End If   
   End Sub
End Module
' The example displays the following output:
'       Window not found.

S’applique à