SafeFileHandle Class

Definition

Represents a wrapper class for a file handle.

C#
[System.Security.SecurityCritical]
public sealed class SafeFileHandle : System.Runtime.InteropServices.SafeHandle
C#
public sealed class SafeFileHandle : Microsoft.Win32.SafeHandles.SafeHandleZeroOrMinusOneIsInvalid
C#
[System.Security.SecurityCritical]
public sealed class SafeFileHandle : Microsoft.Win32.SafeHandles.SafeHandleZeroOrMinusOneIsInvalid
Inheritance
SafeFileHandle
Inheritance
Attributes

Examples

The following code example demonstrates how to open a file using the SafeFileHandle class and the unmanaged CreateFile function.

C#
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;
        }
    }
}

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.

IsInvalid

Gets a value that indicates whether the handle is invalid.

(Inherited from SafeHandleZeroOrMinusOneIsInvalid)

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)

Applies to

Product Versions
.NET Core 1.0, Core 1.1, Core 2.0, Core 2.1, Core 2.2, Core 3.0, Core 3.1, 5, 6, 7, 8, 9
.NET Framework 2.0, 3.0, 3.5, 4.0, 4.5, 4.5.1, 4.5.2, 4.6, 4.6.1, 4.6.2, 4.7, 4.7.1, 4.7.2, 4.8, 4.8.1
.NET Standard 1.3, 1.4, 1.6, 2.0, 2.1
UWP 10.0

See also