SafeFileHandle Class

Definition

Namespace:

Microsoft.Win32.SafeHandles

Assembly:

System.Runtime.dll

Source:

SafeFileHandle.cs

Represents a wrapper class for a file handle.

public ref class SafeFileHandle sealed : Microsoft::Win32::SafeHandles::SafeHandleZeroOrMinusOneIsInvalid

public sealed class SafeFileHandle : Microsoft.Win32.SafeHandles.SafeHandleZeroOrMinusOneIsInvalid

type SafeFileHandle = class
    inherit SafeHandleZeroOrMinusOneIsInvalid

Public NotInheritable Class SafeFileHandle
Inherits SafeHandleZeroOrMinusOneIsInvalid

Inheritance

Object

CriticalFinalizerObject

SafeHandle

SafeHandleZeroOrMinusOneIsInvalid

SafeFileHandle

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(nameof(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 (!handleValue.IsInvalid)
                return handleValue;
            
            return null;
        }
    }
}

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()	Creates a SafeFileHandle around a file handle.
SafeFileHandle(IntPtr, Boolean)	Initializes a new instance of the SafeFileHandle class.

Fields

handle

Specifies the handle to be wrapped. (Inherited from SafeHandle)

Properties

IsAsync	Gets a value that determines if the handle is asynchronous or not.
IsClosed	Gets a value indicating whether the handle is closed. (Inherited from SafeHandle)
IsInvalid	Gets a value that indicates whether the handle is invalid.

Methods

Close()	Marks the handle for releasing and freeing resources. (Inherited from SafeHandle)
DangerousAddRef(Boolean)	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)
GetHashCode()	Serves as the default hash function. (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(IntPtr)	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)

See also

• SafeHandle
• SafeHandleZeroOrMinusOneIsInvalid