IntPtr.Zero Field

Definition

表示已初始化为零的指针或句柄的只读字段。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

此字段的值与 null不等效。The value of this field is not equivalent to null. 使用此字段来有效地确定 IntPtr 的实例是否已设置为非零值。Use this field to efficiently determine whether an instance of IntPtr has been set to a value other than zero.

例如,假设变量 ip 是 IntPtr的实例。For example, assume the variable, ip, is an instance of IntPtr. 您可以通过将它与构造函数返回的值进行比较来确定是否已设置该设置,例如: "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)... ". 但是,调用构造函数以获取未初始化的指针是低效的。However, invoking a constructor to get an uninitialized pointer is inefficient. 更好的做法是编写 "if ip != IntPtr.Zero..." 或 "if !IntPtr.Zero.Equals(ip)..."。It is better to code either " if ip != IntPtr.Zero... ", or " if !IntPtr.Zero.Equals(ip)... ".

从托管代码调用 Windows API 时,如果参数应为指针或 null,则可以传递 IntPtr.Zero 而不是 nullWhen 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. 例如,对 Windows CreateFile 函数的以下调用将为 pSecurityAttributeshTemplateFile 参数值提供 IntPtr.ZeroFor 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

尽管 Zero 等效于包含参数或返回值的 Windows API 函数 null 可以是指针或 null,但 Zeronull不等效。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. null 传递到 IntPtr.Zero.Equals 方法始终返回 falsePassing null to the IntPtr.Zero.Equals method always returns false.

你还可以通过将返回的值与 IntPtr.Zero进行比较来测试返回指针或 null 的 Windows API 函数调用中的 null 返回值。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. 例如,在以下示例中调用 GetWindow 函数尝试检索不存在的窗口的句柄。For example, the call to the GetWindow function in the following example tries to retrieve the handle of a non-existent window. 如果它是从非托管代码调用的,则该函数将返回 null,但从托管代码调用该函数时,它将返回 IntPtr.ZeroIf 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