FileStream.Flush Method

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

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

public override void Flush()

ExceptionCondition
IOException

An I/O error occurred.

ObjectDisposedException

The stream is closed.

This method overrides Stream.Flush.

When you call the FileStream.Flush method, the operating system I/O buffer is also flushed.

A stream’s encoder is not flushed unless you explicitly call Flush or dispose of the object. Setting StreamWriter.AutoFlush to true means that data will be flushed from the buffer to the stream, but the encoder state will not be flushed. This allows the encoder to keep its state (partial characters) so that it can encode the next block of characters correctly. This scenario affects UTF8 and UTF7 where certain characters can only be encoded after the encoder receives the adjacent character or characters.

Because a buffer can be used for either reading or writing, Flush() performs the following two functions:

  • Any data previously written to the buffer is copied to the file and the buffer is cleared except for its encoder state.

  • If BufferedStream.CanSeek is true and data was previously copied from the file to the buffer for reading, the current position within the file is decremented by the number of unread bytes in the buffer. The buffer is then cleared.

Use the Flush(Boolean) method overload when you want to ensure that all buffered data in intermediate file buffers is written to disk.

This code example is part of a larger example provided for the Lock method.

// Update the file. 
case 'W':
    try
    {
        fileStream.Seek(textLength, 
            SeekOrigin.Begin);
        fileStream.Read(
            readText, textLength - 1, byteCount);
        tempString = new String(
            uniEncoding.GetChars(
            readText, textLength - 1, byteCount));
        recordNumber = int.Parse(tempString) + 1;
        fileStream.Seek(
            textLength, SeekOrigin.Begin);
        fileStream.Write(uniEncoding.GetBytes(
            recordNumber.ToString()), 
            0, byteCount);
        fileStream.Flush();
        Console.WriteLine(
            "Record has been updated.");
    }

.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

.NET for Windows Phone apps

Supported in: Windows Phone 8.1, Windows Phone 8, Silverlight 8.1

Windows Phone 8.1, Windows Phone 8, 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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