SafeFileHandle
Class
Definition
Represents a wrapper class for a file handle.
[System.Security.SecurityCritical]
public sealed class SafeFileHandle : Microsoft.Win32.SafeHandles.SafeHandleZeroOrMinusOneIsInvalid
- Inheritance
- Attributes
Inherited Members
System.Object
System.Runtime.InteropServices.SafeHandle
Examples
The following code example demonstrates how to open a file using the SafeFileHandle class and the unmanaged CreateFile function.
using System;
using Microsoft.Win32.SafeHandles;
using System.Runtime.InteropServices;
using System.ComponentModel;
class SafeHandlesExample
{
static void Main()
{
try
{
UnmanagedFileLoader loader = new UnmanagedFileLoader("example.xml");
}
catch (Exception e)
{
Console.WriteLine(e);
}
Console.ReadLine();
}
}
class UnmanagedFileLoader
{
public const short FILE_ATTRIBUTE_NORMAL = 0x80;
public const short INVALID_HANDLE_VALUE = -1;
public const uint GENERIC_READ = 0x80000000;
public const uint GENERIC_WRITE = 0x40000000;
public const uint CREATE_NEW = 1;
public const uint CREATE_ALWAYS = 2;
public const uint OPEN_EXISTING = 3;
// Use interop to call the CreateFile function.
// For more information about CreateFile,
// see the unmanaged MSDN reference library.
[DllImport("kernel32.dll", SetLastError = true, CharSet=CharSet.Unicode)]
static extern SafeFileHandle CreateFile(string lpFileName, uint dwDesiredAccess,
uint dwShareMode, IntPtr lpSecurityAttributes, uint dwCreationDisposition,
uint dwFlagsAndAttributes, IntPtr hTemplateFile);
private SafeFileHandle handleValue = null;
public UnmanagedFileLoader(string Path)
{
Load(Path);
}
public void Load(string Path)
{
if (Path == null || Path.Length == 0)
{
throw new ArgumentNullException("Path");
}
// Try to open the file.
handleValue = CreateFile(Path, GENERIC_WRITE, 0, IntPtr.Zero, OPEN_EXISTING, 0, IntPtr.Zero);
// If the handle is invalid,
// get the last Win32 error
// and throw a Win32Exception.
if (handleValue.IsInvalid)
{
Marshal.ThrowExceptionForHR(Marshal.GetHRForLastWin32Error());
}
}
public SafeFileHandle Handle
{
get
{
// If the handle is valid,
// return it.
if (!handleValue.IsInvalid)
{
return handleValue;
}
else
{
return null;
}
}
}
}
Imports System
Imports Microsoft.Win32.SafeHandles
Imports System.Runtime.InteropServices
Imports System.ComponentModel
Module SafeHandlesExample
Sub Main()
Try
Dim loader As New UnmanagedFileLoader("example.xml")
Catch e As Exception
Console.WriteLine(e)
End Try
Console.ReadLine()
End Sub
End Module
Class UnmanagedFileLoader
Public Const FILE_ATTRIBUTE_NORMAL As Short = &H80
Public Const INVALID_HANDLE_VALUE As Short = -1
Public Const GENERIC_READ As Long = &H80000000
Public Const GENERIC_WRITE As UInteger = &H40000000
Public Const CREATE_NEW As UInteger = 1
Public Const CREATE_ALWAYS As UInteger = 2
Public Const OPEN_EXISTING As UInteger = 3
' Use interop to call the CreateFile function.
' For more information about CreateFile,
' see the unmanaged MSDN reference library.
<DllImport("kernel32.dll", SetLastError:=True, CharSet:=CharSet.Unicode)> _
Private Shared Function CreateFile(ByVal lpFileName As String, ByVal dwDesiredAccess As System.UInt32, ByVal dwShareMode As System.UInt32, ByVal lpSecurityAttributes As IntPtr, ByVal dwCreationDisposition As System.UInt32, ByVal dwFlagsAndAttributes As System.UInt32, ByVal hTemplateFile As IntPtr) As Microsoft.Win32.SafeHandles.SafeFileHandle
End Function
Private handleValue As Microsoft.Win32.SafeHandles.SafeFileHandle = Nothing
Public Sub New(ByVal Path As String)
Load(Path)
End Sub
Public Sub Load(ByVal Path As String)
If Path Is Nothing OrElse Path.Length = 0 Then
Throw New ArgumentNullException("Path")
End If
' Try to open the file.
handleValue = CreateFile(Path, GENERIC_WRITE, 0, IntPtr.Zero, OPEN_EXISTING, 0, IntPtr.Zero)
' If the handle is invalid,
' get the last Win32 error
' and throw a Win32Exception.
If handleValue.IsInvalid Then
Marshal.ThrowExceptionForHR(Marshal.GetHRForLastWin32Error())
End If
End Sub
Public ReadOnly Property Handle() As Microsoft.Win32.SafeHandles.SafeFileHandle
Get
' If the handle is valid,
' return it.
If Not handleValue.IsInvalid Then
Return handleValue
Else
Return Nothing
End If
End Get
End Property
End Class
Remarks
This class is derived from SafeHandleZeroOrMinusOneIsInvalid. A value of 0 or -1 is an invalid file handle.
Important
This type implements the IDisposable interface. When you have finished using the type, you should dispose of it either directly or indirectly. To dispose of the type directly, call its Dispose method in a try/catch block. To dispose of it indirectly, use a language construct such as using (in C#) or Using (in Visual Basic). For more information, see the "Using an Object that Implements IDisposable" section in the IDisposable interface topic.
Constructors
| SafeFileHandle(IntPtr, Boolean) |
Initializes a new instance of the SafeFileHandle class. |
Properties
| IsInvalid |