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FileStream Constructor (String, FileMode, FileAccess, FileShare, Int32, Boolean)

Initializes a new instance of the FileStream class with the specified path, creation mode, read/write and sharing permission, buffer size, and synchronous or asynchronous state.

Namespace:  System.IO
Assembly:  mscorlib (in mscorlib.dll)

'Declaration
Public Sub New ( _
	path As String, _
	mode As FileMode, _
	access As FileAccess, _
	share As FileShare, _
	bufferSize As Integer, _
	useAsync As Boolean _
)

Parameters

path
Type: System.String

A relative or absolute path for the file that the current FileStream object will encapsulate.

mode
Type: System.IO.FileMode

A constant that determines how to open or create the file.

access
Type: System.IO.FileAccess

A constant that determines how the file can be accessed by the FileStream object. This gets the CanRead and CanWrite properties of the FileStream object. CanSeek is true if path specifies a disk file.

share
Type: System.IO.FileShare

A constant that determines how the file will be shared by processes.

bufferSize
Type: System.Int32

A positive Int32 value greater than 0 indicating the buffer size. For bufferSize values between one and eight, the actual buffer size is set to eight bytes.

useAsync
Type: System.Boolean

Specifies whether to use asynchronous I/O or synchronous I/O. However, note that the underlying operating system might not support asynchronous I/O, so when specifying true, the handle might be opened synchronously depending on the platform. When opened asynchronously, the BeginRead and BeginWrite methods perform better on large reads or writes, but they might be much slower for small reads or writes. If the application is designed to take advantage of asynchronous I/O, set the useAsync parameter to true. Using asynchronous I/O correctly can speed up applications by as much as a factor of 10, but using it without redesigning the application for asynchronous I/O can decrease performance by as much as a factor of 10.

ExceptionCondition
ArgumentNullException

path is Nothing.

ArgumentException

path is an empty string (""), contains only white space, or contains one or more invalid characters.

-or-

path refers to a non-file device, such as "con:", "com1:", "lpt1:", etc. in an NTFS environment.

NotSupportedException

path refers to a non-file device, such as "con:", "com1:", "lpt1:", etc. in a non-NTFS environment.

ArgumentOutOfRangeException

bufferSize is negative or zero.

-or-

mode, access, or share contain an invalid value.

FileNotFoundException

The file cannot be found, such as when mode is FileMode.Truncate or FileMode.Open, and the file specified by path does not exist. The file must already exist in these modes.

IOException

An I/O error, such as specifying FileMode.CreateNew when the file specified by path already exists, occurred.

-or-

The system is running Windows 98 or Windows 98 Second Edition and share is set to FileShare.Delete.

-or-

The stream has been closed.

SecurityException

The caller does not have the required permission.

DirectoryNotFoundException

The specified path is invalid, such as being on an unmapped drive.

UnauthorizedAccessException

The access requested is not permitted by the operating system for the specified path, such as when access is Write or ReadWrite and the file or directory is set for read-only access.

PathTooLongException

The specified path, file name, or both exceed the system-defined maximum length. For example, on Windows-based platforms, paths must be less than 248 characters, and file names must be less than 260 characters.

The .NET Framework does not support direct access to physical disks through paths that are device names, such as "\\.\PHYSICALDRIVE0 ".

The path parameter can be a file name, including a file on a Universal Naming Convention (UNC) share.

NoteNote

path is not required to be a file stored on disk; it can be any part of a system that supports access through streams. For example, depending on the system, this class can access a physical device.

CanSeek is true for all FileStream objects that encapsulate files. If path indicates a device that does not support seeking, the CanSeek property on the resulting FileStream is false. For additional information, see CanSeek.

Caution noteCaution

When you compile a set of characters with a particular cultural setting and retrieve those same characters with a different cultural setting, the characters might not be interpretable, and could cause an exception to be thrown.

For a list of common file and directory operations, see Common I/O Tasks.

The following code example shows how to asynchronously write data to a file and then verify that the data was written correctly. A State object is created to pass information from the main thread to the EndReadCallback and EndWriteCallback methods.

Imports System
Imports System.IO
Imports System.Threading

Class FStream

    Shared Sub Main()

        ' Create a synchronization object that gets  
        ' signaled when verification is complete. 
        Dim manualEvent As New ManualResetEvent(False)

        ' Create random data to write to the file. 
        Dim writeArray(100000) As Byte 
        Dim randomGenerator As New Random()
        randomGenerator.NextBytes(writeArray)

        Dim fStream As New FileStream("Test#@@#.dat", _
            FileMode.Create, FileAccess.ReadWrite, _
            FileShare.None, 4096, True)

        ' Check that the FileStream was opened asynchronously. 
        If fStream.IsAsync = True
            Console.WriteLine("fStream was opened asynchronously.")
        Else
            Console.WriteLine("fStream was not opened asynchronously.")
        End If 

        ' Asynchronously write to the file. 
        Dim asyncResult As IAsyncResult = fStream.BeginWrite( _
            writeArray, 0, writeArray.Length, _
            AddressOf EndWriteCallback , _
            New State(fStream, writeArray, manualEvent))

        ' Concurrently do other work and then wait 
        ' for the data to be written and verified.
        manualEvent.WaitOne(5000, False)
    End Sub 

    ' When BeginWrite is finished writing data to the file, the 
    ' EndWriteCallback method is called to end the asynchronous  
    ' write operation and then read back and verify the data. 
    Private Shared Sub EndWriteCallback(asyncResult As IAsyncResult)
        Dim tempState As State = _
            DirectCast(asyncResult.AsyncState, State)
        Dim fStream As FileStream = tempState.FStream
        fStream.EndWrite(asyncResult)

        ' Asynchronously read back the written data.
        fStream.Position = 0
        asyncResult = fStream.BeginRead( _ 
            tempState.ReadArray, 0 , tempState.ReadArray.Length, _
            AddressOf EndReadCallback, tempState)

        ' Concurrently do other work, such as  
        ' logging the write operation. 
    End Sub 

    ' When BeginRead is finished reading data from the file, the  
    ' EndReadCallback method is called to end the asynchronous  
    ' read operation and then verify the data. 
   Private Shared Sub EndReadCallback(asyncResult As IAsyncResult)
        Dim tempState As State = _
            DirectCast(asyncResult.AsyncState, State)
        Dim readCount As Integer = _
            tempState.FStream.EndRead(asyncResult)

        Dim i As Integer = 0
        While(i < readCount)
            If(tempState.ReadArray(i) <> tempState.WriteArray(i))
                Console.WriteLine("Error writing data.")
                tempState.FStream.Close()
                Return 
            End If
            i += 1
        End While

        Console.WriteLine("The data was written to {0} and " & _
            "verified.", tempState.FStream.Name)
        tempState.FStream.Close()

        ' Signal the main thread that the verification is finished.
        tempState.ManualEvent.Set()
    End Sub 

    ' Maintain state information to be passed to  
    ' EndWriteCallback and EndReadCallback. 
    Private Class State

        ' fStreamValue is used to read and write to the file. 
        Dim fStreamValue As FileStream

        ' writeArrayValue stores data that is written to the file. 
        Dim writeArrayValue As Byte()

        ' readArrayValue stores data that is read from the file. 
        Dim readArrayValue As Byte()

        ' manualEvent signals the main thread  
        ' when verification is complete. 
        Dim manualEventValue As ManualResetEvent 

        Sub New(aStream As FileStream, anArray As Byte(), _
            manualEvent As ManualResetEvent)

            fStreamValue     = aStream
            writeArrayValue  = anArray
            manualEventValue = manualEvent
            readArrayValue   = New Byte(anArray.Length - 1){}
        End Sub     

            Public ReadOnly Property FStream() As FileStream
                Get 
                    Return fStreamValue
                End Get 
            End Property 

            Public ReadOnly Property WriteArray() As Byte()
                Get 
                    Return writeArrayValue
                End Get 
            End Property 

            Public ReadOnly Property ReadArray() As Byte()
                Get 
                    Return readArrayValue
                End Get 
            End Property 

            Public ReadOnly Property ManualEvent() As ManualResetEvent
                Get 
                    Return manualEventValue
                End Get 
            End Property 
    End Class  

End Class

.NET Framework

Supported in: 4.5.2, 4.5.1, 4.5, 4, 3.5, 3.0, 2.0, 1.1, 1.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

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