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SafeFileHandle Class

Represents a wrapper class for a file handle.

Namespace:  Microsoft.Win32.SafeHandles
Assembly:  mscorlib (in mscorlib.dll)

public sealed class SafeFileHandle : SafeHandleZeroOrMinusOneIsInvalid

The SafeFileHandle type exposes the following members.

  NameDescription
Public methodSafeFileHandleInitializes a new instance of the SafeFileHandle class.
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  NameDescription
Public propertyIsClosedGets a value indicating whether the handle is closed. (Inherited from SafeHandle.)
Public propertyIsInvalidGets a value that indicates whether the handle is invalid. (Inherited from SafeHandleZeroOrMinusOneIsInvalid.)
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  NameDescription
Public methodCloseMarks the handle for releasing and freeing resources. (Inherited from SafeHandle.)
Public methodDangerousAddRefManually increments the reference counter on SafeHandle instances. (Inherited from SafeHandle.)
Public methodDangerousGetHandleReturns the value of the handle field. (Inherited from SafeHandle.)
Public methodDangerousReleaseManually decrements the reference counter on a SafeHandle instance. (Inherited from SafeHandle.)
Public methodDispose()Releases all resources used by the SafeHandle class. (Inherited from SafeHandle.)
Protected methodDispose(Boolean)Releases the unmanaged resources used by the SafeHandle class specifying whether to perform a normal dispose operation. (Inherited from SafeHandle.)
Public methodEquals(Object)Determines whether the specified Object is equal to the current Object. (Inherited from Object.)
Protected methodFinalizeFrees all resources associated with the handle. (Inherited from SafeHandle.)
Public methodGetHashCodeServes as a hash function for a particular type. (Inherited from Object.)
Public methodGetTypeGets the Type of the current instance. (Inherited from Object.)
Protected methodMemberwiseCloneCreates a shallow copy of the current Object. (Inherited from Object.)
Protected methodReleaseHandleWhen overridden in a derived class, executes the code required to free the handle. (Inherited from SafeHandle.)
Protected methodSetHandleSets the handle to the specified pre-existing handle. (Inherited from SafeHandle.)
Public methodSetHandleAsInvalidMarks a handle as no longer used. (Inherited from SafeHandle.)
Public methodToStringReturns a string that represents the current object. (Inherited from Object.)
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  NameDescription
Protected fieldhandleSpecifies the handle to be wrapped. (Inherited from SafeHandle.)
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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.


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;
            }
        }

    }

}


.NET Framework

Supported in: 4, 3.5, 3.0, 2.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

  • 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.

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

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