SafeFileHandle Class
Represents a wrapper class for a file handle.
System.Runtime.ConstrainedExecution.CriticalFinalizerObject
System.Runtime.InteropServices.SafeHandle
Microsoft.Win32.SafeHandles.SafeHandleZeroOrMinusOneIsInvalid
Microsoft.Win32.SafeHandles.SafeFileHandle
Assembly: mscorlib (in mscorlib.dll)
The SafeFileHandle type exposes the following members.
| Name | Description | |
|---|---|---|
![]() | IsClosed | Gets a value indicating whether the handle is closed. (Inherited from SafeHandle.) |
![]() | IsInvalid | Gets a value that indicates whether the handle is invalid. (Inherited from SafeHandleZeroOrMinusOneIsInvalid.) |
| Name | Description | |
|---|---|---|
![]() | Close | Marks the handle for releasing and freeing resources. (Inherited from SafeHandle.) |
![]() | DangerousAddRef | Manually increments the reference counter on SafeHandle instances. (Inherited from SafeHandle.) |
![]() | DangerousGetHandle | Returns the value of the handle field. (Inherited from SafeHandle.) |
![]() | DangerousRelease | Manually decrements the reference counter on a SafeHandle instance. (Inherited from SafeHandle.) |
![]() | Dispose | Releases all resources used by the SafeHandle class. (Inherited from SafeHandle.) |
![]() | Dispose(Boolean) | Releases the unmanaged resources used by the SafeHandle class specifying whether to perform a normal dispose operation. (Inherited from SafeHandle.) |
![]() | Equals(Object) | Determines whether the specified Object is equal to the current Object. (Inherited from Object.) |
![]() | Finalize | Frees all resources associated with the handle. (Inherited from SafeHandle.) |
![]() | GetHashCode | Serves as a hash function for a particular type. (Inherited from Object.) |
![]() | GetType | Gets the Type of the current instance. (Inherited from Object.) |
![]() | MemberwiseClone | Creates a shallow copy of the current Object. (Inherited from Object.) |
![]() | ReleaseHandle | When overridden in a derived class, executes the code required to free the handle. (Inherited from SafeHandle.) |
![]() | SetHandle | Sets the handle to the specified pre-existing handle. (Inherited from SafeHandle.) |
![]() | SetHandleAsInvalid | Marks a handle as no longer used. (Inherited from SafeHandle.) |
![]() | ToString | Returns a string that represents the current object. (Inherited from Object.) |
This class is derived from SafeHandleZeroOrMinusOneIsInvalid. A value of 0 or -1 is an invalid file handle.
The following code example demonstrates how to open a file using the SafeFileHandle class and the unmanaged CreateFile function.
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
- SecurityCriticalAttribute
requires full trust for the immediate caller. This member cannot be used by partially trusted or transparent code.
Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2
The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.



