IntPtr.Zero Field

Definition

Campo de solo lectura que representa un puntero o identificador que se inicializó en cero.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 

Field Value

IntPtr

Remarks

El valor de este campo no es equivalente a null.The value of this field is not equivalent to null. Utilice este campo para determinar de forma eficaz si una instancia de IntPtr se ha establecido en un valor distinto de cero.Use this field to efficiently determine whether an instance of IntPtr has been set to a value other than zero.

Por ejemplo, supongamos que la variable IP es una instancia de IntPtr.For example, assume the variable, ip, is an instance of IntPtr. Puede determinar si se ha establecido al compararlo con el valor devuelto por un constructor, por ejemplo: "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)... ". Sin embargo, invocar un constructor para obtener un puntero no inicializado es ineficaz.However, invoking a constructor to get an uninitialized pointer is inefficient. Es mejor codificar "if ip != IntPtr.Zero..." o "if !IntPtr.Zero.Equals(ip)...".It is better to code either " if ip != IntPtr.Zero... ", or " if !IntPtr.Zero.Equals(ip)... ".

Cuando se llama a la API de Windows desde código administrado, se puede pasar IntPtr.Zero en lugar de null si se espera que un argumento sea un puntero o un null.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. Por ejemplo, la siguiente llamada a la función de Windows CreateFile proporciona IntPtr.Zero para los valores de los argumentos pSecurityAttributes y hTemplateFile.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.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)

Note

Aunque Zero es equivalente a null para las funciones de la API de Windows con parámetros o valores devueltos que pueden ser punteros o null, Zero no es equivalente a null.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. Pasar null al método IntPtr.Zero.Equals siempre devuelve false.Passing null to the IntPtr.Zero.Equals method always returns false.

También puede probar una null valor devuelto de las llamadas de función de la API de Windows que devuelven un puntero o un null comparando el valor devuelto con 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. Por ejemplo, la llamada a la función GetWindow en el ejemplo siguiente intenta recuperar el identificador de una ventana que no existe.For example, the call to the GetWindow function in the following example tries to retrieve the handle of a non-existent window. Si se llama desde código no administrado, la función devolvería null, pero cuando se llama desde código administrado, devuelve IntPtr.Zero.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.

Applies to