SafeFileHandle クラスとは何？わかりやすく解説 Weblio辞書

.NET Framework クラスライブラリリファレンス

索引トップ用語の索引ランキング

SafeFileHandle クラス

メモ : このクラスは、.NET Framework version 2.0 で新しく追加されたものです。

ファイルハンドルのラッパークラスを表します。このクラスは継承できません。

名前空間: Microsoft.Win32.SafeHandles
アセンブリ: mscorlib (mscorlib.dll 内)
構文

Visual Basic (宣言)

Public NotInheritable Class
 SafeFileHandle
    Inherits SafeHandleZeroOrMinusOneIsInvalid

Visual Basic (使用法)

Dim instance As SafeFileHandle

public sealed class SafeFileHandle : SafeHandleZeroOrMinusOneIsInvalid

C++

public ref class SafeFileHandle sealed : public
 SafeHandleZeroOrMinusOneIsInvalid

public final class SafeFileHandle extends SafeHandleZeroOrMinusOneIsInvalid

JScript

public final class SafeFileHandle extends
 SafeHandleZeroOrMinusOneIsInvalid

解説

このクラスは、SafeHandleZeroOrMinusOneIsInvalid の派生クラスです。値 0 または -1 は無効なファイルハンドルです。

使用例

SafeFileHandle クラスおよび CreateFile アンマネージ関数を使用してファイルを開く方法のコード例を次に示します。

Visual Basic

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)>
 _
    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 SafeFileHandle

    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.
        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.GetLastWin32Error())
        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

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)]
    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.GetLastWin32Error());
        }
    }

    public SafeFileHandle Handle
    {
        get
        {
            // If the handle is valid,
            // return it.
            if (!handleValue.IsInvalid)
            {
                return handleValue;
            }
            else
            {
                return null;
            }
        }

    }

}

継承階層

System.Object
   System.Runtime.ConstrainedExecution.CriticalFinalizerObject
     System.Runtime.InteropServices.SafeHandle
       Microsoft.Win32.SafeHandles.SafeHandleZeroOrMinusOneIsInvalid
        Microsoft.Win32.SafeHandles.SafeFileHandle

スレッドセーフ

この型の public static (Visual Basic では Shared) メンバはすべて、スレッドセーフです。インスタンスメンバの場合は、スレッドセーフであるとは限りません。