IntPtr.Zero Field
Definition
Important
Some information relates to prerelease product that may be substantially modified before it’s released. Microsoft makes no warranties, express or implied, with respect to the information provided here.
A read-only field that represents a signed integer 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
nativeint
Remarks
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 uninitialized 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)
open Microsoft.Win32.SafeHandles
open System
open System.Runtime.InteropServices
let GENERIC_READ = 0x80000000u
let OPEN_EXISTING = 3u
let FILE_ATTRIBUTE_NORMAL = 128u
let FILE_FLAG_OVERLAPPED = 0x40000000u
[<DllImport("kernel32.dll", SetLastError = true, CharSet = CharSet.Unicode)>]
extern SafeFileHandle CreateFile(
string lpFileName, uint dwDesiredAccess, uint dwShareMode,
nativeint pSecurityAttributes, uint dwCreationDisposition,
uint dwFlagsAndAttributes, nativeint hTemplateFile)
let hnd =
CreateFile("CallOfTheWild.txt", GENERIC_READ, 0u,
IntPtr.Zero, OPEN_EXISTING,
FILE_ATTRIBUTE_NORMAL ||| FILE_FLAG_OVERLAPPED,
IntPtr.Zero)
if hnd.IsInvalid then
let ex = Marshal.GetExceptionForHR(Marshal.GetHRForLastWin32Error())
printfn $"Attempt to open file failed:\n {ex.Message}"
else
printfn "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
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.
open System
open System.Runtime.InteropServices
let GW_OWNER = 4
[<DllImport("user32", CharSet=CharSet.Auto, SetLastError=true, ExactSpelling=true)>]
extern IntPtr GetWindow(nativeint hwnd, int wFlag)
let hwnd = IntPtr 3
let hOwner = GetWindow(hwnd, GW_OWNER)
if hOwner = IntPtr.Zero then
printfn "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
Pripomienky
https://aka.ms/ContentUserFeedback.
Pripravujeme: V priebehu roka 2024 postupne zrušíme službu Problémy v službe GitHub ako mechanizmus pripomienok týkajúcich sa obsahu a nahradíme ju novým systémom pripomienok. Ďalšie informácie nájdete na stránke:Odoslať a zobraziť pripomienky pre