IntPtr.Zero フィールド

定義

0 に初期化されたポインターまたはハンドルを表す読み取り専用フィールド。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 

フィールド値

注釈

このフィールドの値は nullと同じではありません。The value of this field is not equivalent to null. このフィールドを使用すると、IntPtr のインスタンスが0以外の値に設定されているかどうかを効率的に判断できます。Use this field to efficiently determine whether an instance of IntPtr has been set to a value other than zero.

たとえば、という変数 (ip) が IntPtrのインスタンスであるとします。For example, assume the variable, ip, is an instance of IntPtr. コンストラクターによって返された値と比較することによって設定されているかどうかを判断できます (例: "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)... ". ただし、初期化されていないポインターを取得するコンストラクターを呼び出すことは、効率的ではありません。However, invoking a constructor to get an uninitialized pointer is inefficient. "if ip != IntPtr.Zero..." または "if !IntPtr.Zero.Equals(ip)..." のいずれかのコードを記述することをお勧めします。It is better to code either " if ip != IntPtr.Zero... ", or " if !IntPtr.Zero.Equals(ip)... ".

マネージコードから Windows API を呼び出すときに、引数がポインターまたは nullのいずれかであると想定されている場合は、null ではなく IntPtr.Zero を渡すことができます。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. たとえば、次の Windows CreateFile 関数の呼び出しでは、pSecurityAttributeshTemplateFile の引数の値に IntPtr.Zero を指定します。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)

注意

Zero は、パラメーターまたは戻り値を持つ、ポインターまたは nullの Windows API 関数の null に相当しますが、Zeronullとは異なります。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. IntPtr.Zero.Equals メソッドに null を渡すと、常に falseが返されます。Passing null to the IntPtr.Zero.Equals method always returns false.

また、戻り値と IntPtr.Zeroを比較することによって、ポインターまたは null のいずれかを返す Windows API 関数呼び出しから null 戻り値をテストすることもできます。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. たとえば、次の例の GetWindow 関数の呼び出しでは、存在しないウィンドウのハンドルを取得しようとします。For example, the call to the GetWindow function in the following example tries to retrieve the handle of a non-existent window. アンマネージコードから呼び出された場合、関数は nullを返しますが、マネージコードから呼び出されると、IntPtr.Zeroを返します。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.

適用対象