SafeFileHandle Constructors

Definition

Namespace:

Microsoft.Win32.SafeHandles

Assembly:

System.Runtime.dll

Overloads

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

SafeFileHandle()

Source:

SafeFileHandle.Unix.cs

Creates a SafeFileHandle around a file handle.

public:
 SafeFileHandle();

public SafeFileHandle ();

Public Sub New ()

SafeFileHandle(IntPtr, Boolean)

Source:

SafeFileHandle.cs

Initializes a new instance of the SafeFileHandle class.

public:
 SafeFileHandle(IntPtr preexistingHandle, bool ownsHandle);

public SafeFileHandle (IntPtr preexistingHandle, bool ownsHandle);

new Microsoft.Win32.SafeHandles.SafeFileHandle : nativeint * bool -> Microsoft.Win32.SafeHandles.SafeFileHandle

Public Sub New (preexistingHandle As IntPtr, ownsHandle As Boolean)

Parameters

preexistingHandle

IntPtr

nativeint

An IntPtr object that represents the pre-existing handle to use.

ownsHandle

Boolean

true to reliably release the handle during the finalization phase; false to prevent reliable release (not recommended).

Examples

The following example demonstrates how to open a file by 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 IntPtr 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.
        IntPtr ptr = CreateFile(Path, GENERIC_WRITE, 0, IntPtr.Zero, OPEN_EXISTING, 0, IntPtr.Zero);

        handleValue = new SafeFileHandle(ptr, true);

        // 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 Microsoft.Win32.SafeHandles
Imports System.Runtime.InteropServices
Imports System.ComponentModel



Class SafeHandlesExample


    Shared Sub Main()
        Try

            Dim loader As New UnmanagedFileLoader("example.xml")


        Catch e As Exception
            Console.WriteLine(e)
        End Try
        Console.ReadLine()

    End Sub
End Class


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 IntPtr

    End Function

    Private handleValue As SafeFileHandle = Nothing



    Public Sub New(ByVal Path As String)
        Load(Path)

    End Sub


    Public Sub Load(ByVal Path As String)
        If Path Is Nothing AndAlso Path.Length = 0 Then
            Throw New ArgumentNullException("Path")
        End If

        ' Try to open the file.

        Dim ptr As IntPtr = CreateFile(Path, GENERIC_WRITE, 0, IntPtr.Zero, OPEN_EXISTING, 0, IntPtr.Zero)

        handleValue = New SafeFileHandle(ptr, True)
        ' 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 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

See also

• SafeHandle