FileStream Class

Definition

Provides a Stream for a file, supporting both synchronous and asynchronous read and write operations.

[System.Runtime.InteropServices.ComVisible(true)]
public class FileStream : System.IO.Stream
Inheritance
Derived
Attributes

Examples

The following example demonstrates some of the FileStream constructors.

using namespace System;
using namespace System::IO;
using namespace System::Text;

void AddText( FileStream^ fs, String^ value )
{
   array<Byte>^info = (gcnew UTF8Encoding( true ))->GetBytes( value );
   fs->Write( info, 0, info->Length );
}

int main()
{
   String^ path = "c:\\temp\\MyTest.txt";
   
   // Delete the file if it exists.
   if ( File::Exists( path ) )
   {
      File::Delete( path );
   }

   //Create the file.
   {
      FileStream^ fs = File::Create( path );
      try
      {
         AddText( fs, "This is some text" );
         AddText( fs, "This is some more text," );
         AddText( fs, "\r\nand this is on a new line" );
         AddText( fs, "\r\n\r\nThe following is a subset of characters:\r\n" );
         for ( int i = 1; i < 120; i++ )
         {
            AddText( fs, Convert::ToChar( i ).ToString() );
            
            //Split the output at every 10th character.
            if ( Math::IEEERemainder( Convert::ToDouble( i ), 10 ) == 0 )
            {
               AddText( fs, "\r\n" );
            }
         }
      }
      finally
      {
         if ( fs )
            delete (IDisposable^)fs;
      }
   }
   
   //Open the stream and read it back.
   {
      FileStream^ fs = File::OpenRead( path );
      try
      {
         array<Byte>^b = gcnew array<Byte>(1024);
         UTF8Encoding^ temp = gcnew UTF8Encoding( true );
         while ( fs->Read( b, 0, b->Length ) > 0 )
         {
            Console::WriteLine( temp->GetString( b ) );
         }
      }
      finally
      {
         if ( fs )
            delete (IDisposable^)fs;
      }
   }
}
using System;
using System.IO;
using System.Text;

class Test
{

    public static void Main()
    {
        string path = @"c:\temp\MyTest.txt";

        // Delete the file if it exists.
        if (File.Exists(path))
        {
            File.Delete(path);
        }

        //Create the file.
        using (FileStream fs = File.Create(path))
        {
            AddText(fs, "This is some text");
            AddText(fs, "This is some more text,");
            AddText(fs, "\r\nand this is on a new line");
            AddText(fs, "\r\n\r\nThe following is a subset of characters:\r\n");

            for (int i=1;i < 120;i++)
            {
                AddText(fs, Convert.ToChar(i).ToString());

            }
        }

        //Open the stream and read it back.
        using (FileStream fs = File.OpenRead(path))
        {
            byte[] b = new byte[1024];
            UTF8Encoding temp = new UTF8Encoding(true);
            while (fs.Read(b,0,b.Length) > 0)
            {
                Console.WriteLine(temp.GetString(b));
            }
        }
    }

    private static void AddText(FileStream fs, string value)
    {
        byte[] info = new UTF8Encoding(true).GetBytes(value);
        fs.Write(info, 0, info.Length);
    }
}
Imports System
Imports System.IO
Imports System.Text

Public Class Test

    Public Shared Sub Main()
        Dim path As String = "c:\temp\MyTest.txt"

        ' Delete the file if it exists.
        If File.Exists(path) Then
            File.Delete(path)
        End If

        'Create the file.
        Dim fs As FileStream = File.Create(path)

        AddText(fs, "This is some text")
        AddText(fs, "This is some more text,")
        AddText(fs, Environment.NewLine & "and this is on a new line")
        AddText(fs, Environment.NewLine & Environment.NewLine)
        AddText(fs, "The following is a subset of characters:" & Environment.NewLine)

        Dim i As Integer

        For i = 1 To 120
            AddText(fs, Convert.ToChar(i).ToString())

        Next

        fs.Close()

        'Open the stream and read it back.
        fs = File.OpenRead(path)
        Dim b(1024) As Byte
        Dim temp As UTF8Encoding = New UTF8Encoding(True)

        Do While fs.Read(b, 0, b.Length) > 0
            Console.WriteLine(temp.GetString(b))
        Loop

        fs.Close()
    End Sub

    Private Shared Sub AddText(ByVal fs As FileStream, ByVal value As String)
        Dim info As Byte() = New UTF8Encoding(True).GetBytes(value)
        fs.Write(info, 0, info.Length)
    End Sub
End Class

The following example shows how to write to a file asynchronously. This code runs in a WPF app that has a TextBlock named UserInput and a button hooked up to a Click event handler that is named Button_Click. The file path needs to be changed to a file than exits on the computer.

using System;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;
using System.IO;

namespace WpfApplication1
{
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
        }

        private async void Button_Click(object sender, RoutedEventArgs e)
        {
            UnicodeEncoding uniencoding = new UnicodeEncoding();
            string filename = @"c:\Users\exampleuser\Documents\userinputlog.txt";
           
            byte[] result = uniencoding.GetBytes(UserInput.Text);
            
            using (FileStream SourceStream = File.Open(filename, FileMode.OpenOrCreate))
            {
                SourceStream.Seek(0, SeekOrigin.End);
                await SourceStream.WriteAsync(result, 0, result.Length);
            }
        }
    }
}
Imports System.IO
Imports System.Text

Class MainWindow
    Private Async Sub Button_Click(sender As Object, e As RoutedEventArgs)
        Dim uniencoding As UnicodeEncoding = New UnicodeEncoding()
        Dim filename As String = "c:\Users\exampleuser\Documents\userinputlog.txt"

        Dim result As Byte() = uniencoding.GetBytes(UserInput.Text)

        Using SourceStream As FileStream = File.Open(filename, FileMode.OpenOrCreate)
            SourceStream.Seek(0, SeekOrigin.End)
            Await SourceStream.WriteAsync(result, 0, result.Length)
        End Using
    End Sub
End Class

Remarks

Note

To view the .NET Framework source code for this type, see the Reference Source. You can browse through the source code online, download the reference for offline viewing, and step through the sources (including patches and updates) during debugging; see instructions.

Use the FileStream class to read from, write to, open, and close files on a file system, and to manipulate other file-related operating system handles, including pipes, standard input, and standard output. You can use the Read, Write, CopyTo, and Flush methods to perform synchronous operations, or the ReadAsync, WriteAsync, CopyToAsync, and FlushAsync methods to perform asynchronous operations. Use the asynchronous methods to perform resource-intensive file operations without blocking the main thread. This performance consideration is particularly important in a Windows 8.x Store app or desktop app where a time-consuming stream operation can block the UI thread and make your app appear as if it is not working. FileStream buffers input and output for better performance.

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.

The IsAsync property detects whether the file handle was opened asynchronously. You specify this value when you create an instance of the FileStream class using a constructor that has an isAsync, useAsync, or options parameter. When the property is true, the stream utilizes overlapped I/O to perform file operations asynchronously. However, the IsAsync property does not have to be true to call the ReadAsync, WriteAsync, or CopyToAsync method. When the IsAsync property is false and you call the asynchronous read and write operations, the UI thread is still not blocked, but the actual I/O operation is performed synchronously.

The Seek method supports random access to files. Seek allows the read/write position to be moved to any position within the file. This is done with byte offset reference point parameters. The byte offset is relative to the seek reference point, which can be the beginning, the current position, or the end of the underlying file, as represented by the three members of the SeekOrigin enumeration.

Note

Disk files always support random access. At the time of construction, the CanSeek property value is set to true or false depending on the underlying file type.If the underlying file type is FILE_TYPE_DISK, as defined in winbase.h, the CanSeek property value is true. Otherwise, the CanSeek property value is false.

If a process terminates with part of a file locked or closes a file that has outstanding locks, the behavior is undefined.

For directory operations and other file operations, see the File, Directory, and Path classes. The File class is a utility class that has static methods primarily for the creation of FileStream objects based on file paths. The MemoryStream class creates a stream from a byte array and is similar to the FileStream class.

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

Detection of Stream Position Changes

When a FileStream object does not have an exclusive hold on its handle, another thread could access the file handle concurrently and change the position of the operating system's file pointer that is associated with the file handle. In this case, the cached position in the FileStream object and the cached data in the buffer could be compromised. The FileStream object routinely performs checks on methods that access the cached buffer to ensure that the operating system's handle position is the same as the cached position used by the FileStream object.

If an unexpected change in the handle position is detected in a call to the Read method, the .NET Framework discards the contents of the buffer and reads the stream from the file again. This can affect performance, depending on the size of the file and any other processes that could affect the position of the file stream.

If an unexpected change in the handle position is detected in a call to the Write method, the contents of the buffer are discarded and an IOException exception is thrown.

A FileStream object will not have an exclusive hold on its handle when either the SafeFileHandle property is accessed to expose the handle or the FileStream object is given the SafeFileHandle property in its constructor.

Constructors

FileStream(SafeFileHandle, FileAccess)

Initializes a new instance of the FileStream class for the specified file handle, with the specified read/write permission.

FileStream(String, FileMode, FileSystemRights, FileShare, Int32, FileOptions, FileSecurity)

Initializes a new instance of the FileStream class with the specified path, creation mode, access rights and sharing permission, the buffer size, additional file options, access control and audit security.

FileStream(String, FileMode, FileSystemRights, FileShare, Int32, FileOptions)

Initializes a new instance of the FileStream class with the specified path, creation mode, access rights and sharing permission, the buffer size, and additional file options.

FileStream(String, FileMode, FileAccess, FileShare, Int32, FileOptions)

Initializes a new instance of the FileStream class with the specified path, creation mode, read/write and sharing permission, the access other FileStreams can have to the same file, the buffer size, and additional file options.

FileStream(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.

FileStream(IntPtr, FileAccess, Boolean, Int32, Boolean)

Initializes a new instance of the FileStream class for the specified file handle, with the specified read/write permission, FileStream instance ownership, buffer size, and synchronous or asynchronous state.

FileStream(String, FileMode, FileAccess, FileShare)

Initializes a new instance of the FileStream class with the specified path, creation mode, read/write permission, and sharing permission.

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

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

FileStream(SafeFileHandle, FileAccess, Int32, Boolean)

Initializes a new instance of the FileStream class for the specified file handle, with the specified read/write permission, buffer size, and synchronous or asynchronous state.

FileStream(String, FileMode, FileAccess)

Initializes a new instance of the FileStream class with the specified path, creation mode, and read/write permission.

FileStream(IntPtr, FileAccess, Boolean)

Initializes a new instance of the FileStream class for the specified file handle, with the specified read/write permission and FileStream instance ownership.

FileStream(SafeFileHandle, FileAccess, Int32)

Initializes a new instance of the FileStream class for the specified file handle, with the specified read/write permission, and buffer size.

FileStream(String, FileMode)

Initializes a new instance of the FileStream class with the specified path and creation mode.

FileStream(IntPtr, FileAccess)

Initializes a new instance of the FileStream class for the specified file handle, with the specified read/write permission.

FileStream(IntPtr, FileAccess, Boolean, Int32)

Initializes a new instance of the FileStream class for the specified file handle, with the specified read/write permission, FileStream instance ownership, and buffer size.

Properties

CanRead

Gets a value indicating whether the current stream supports reading.

CanSeek

Gets a value indicating whether the current stream supports seeking.

CanWrite

Gets a value indicating whether the current stream supports writing.

Handle

Gets the operating system file handle for the file that the current FileStream object encapsulates.

IsAsync

Gets a value indicating whether the FileStream was opened asynchronously or synchronously.

Length

Gets the length in bytes of the stream.

Name

Gets the name of the FileStream that was passed to the constructor.

Position

Gets or sets the current position of this stream.

SafeFileHandle

Gets a SafeFileHandle object that represents the operating system file handle for the file that the current FileStream object encapsulates.

Methods

BeginRead(Byte[], Int32, Int32, AsyncCallback, Object)

Begins an asynchronous read operation. (Consider using ReadAsync(Byte[], Int32, Int32, CancellationToken) instead.)

BeginWrite(Byte[], Int32, Int32, AsyncCallback, Object)

Begins an asynchronous write operation. (Consider using WriteAsync(Byte[], Int32, Int32, CancellationToken) instead.)

Dispose(Boolean)

Releases the unmanaged resources used by the FileStream and optionally releases the managed resources.

EndRead(IAsyncResult)

Waits for the pending asynchronous read operation to complete. (Consider using ReadAsync(Byte[], Int32, Int32, CancellationToken) instead.)

EndWrite(IAsyncResult)

Ends an asynchronous write operation and blocks until the I/O operation is complete. (Consider using WriteAsync(Byte[], Int32, Int32, CancellationToken) instead.)

Finalize()

Ensures that resources are freed and other cleanup operations are performed when the garbage collector reclaims the FileStream.

Flush()

Clears buffers for this stream and causes any buffered data to be written to the file.

Flush(Boolean)

Clears buffers for this stream and causes any buffered data to be written to the file, and also clears all intermediate file buffers.

FlushAsync(CancellationToken)

Asynchronously clears all buffers for this stream, causes any buffered data to be written to the underlying device, and monitors cancellation requests.

GetAccessControl()

Gets a FileSecurity object that encapsulates the access control list (ACL) entries for the file described by the current FileStream object.

Lock(Int64, Int64)

Prevents other processes from reading from or writing to the FileStream.

Read(Byte[], Int32, Int32)

Reads a block of bytes from the stream and writes the data in a given buffer.

ReadAsync(Byte[], Int32, Int32, CancellationToken)

Asynchronously reads a sequence of bytes from the current stream, advances the position within the stream by the number of bytes read, and monitors cancellation requests.

ReadByte()

Reads a byte from the file and advances the read position one byte.

Seek(Int64, SeekOrigin)

Sets the current position of this stream to the given value.

SetAccessControl(FileSecurity)

Applies access control list (ACL) entries described by a FileSecurity object to the file described by the current FileStream object.

SetLength(Int64)

Sets the length of this stream to the given value.

Unlock(Int64, Int64)

Allows access by other processes to all or part of a file that was previously locked.

Write(Byte[], Int32, Int32)

Writes a block of bytes to the file stream.

WriteAsync(Byte[], Int32, Int32, CancellationToken)

Asynchronously writes a sequence of bytes to the current stream, advances the current position within this stream by the number of bytes written, and monitors cancellation requests.

WriteByte(Byte)

Writes a byte to the current position in the file stream.

CanTimeout Inherited from Stream
Close() Inherited from Stream
CopyTo(Stream) Inherited from Stream
CopyTo(Stream, Int32) Inherited from Stream
CopyToAsync(Stream) Inherited from Stream
CopyToAsync(Stream, Int32) Inherited from Stream
CopyToAsync(Stream, Int32, CancellationToken) Inherited from Stream
CreateWaitHandle() Inherited from Stream
Dispose() Inherited from Stream
FlushAsync() Inherited from Stream
Null Inherited from Stream
ObjectInvariant() Inherited from Stream
ReadAsync(Byte[], Int32, Int32) Inherited from Stream
ReadTimeout Inherited from Stream
Synchronized(Stream) Inherited from Stream
WriteAsync(Byte[], Int32, Int32) Inherited from Stream
WriteTimeout Inherited from Stream
CreateObjRef(Type) Inherited from MarshalByRefObject
GetLifetimeService() Inherited from MarshalByRefObject
InitializeLifetimeService() Inherited from MarshalByRefObject
MemberwiseClone(Boolean) Inherited from MarshalByRefObject
Equals(Object) Inherited from Object
Equals(Object, Object) Inherited from Object
GetHashCode() Inherited from Object
GetType() Inherited from Object
MemberwiseClone() Inherited from Object
ReferenceEquals(Object, Object) Inherited from Object
ToString() Inherited from Object

Extension Methods

GetAccessControl(FileStream)
SetAccessControl(FileStream, FileSecurity)

Applies to

See Also