CODEWITHSUNDEEP
c#filestreamstreamwriterflushbufferedstream
MciprianM
MciprianM

Reputation: 513

Why doesn't text get written to disk?

I have the following C# code:

private const int APPENDBUFFERSIZE = 65536;
private StreamWriter _streamWriter;
private FileStream _fileStream;
private BufferedStream _bufferedStream;

public void Open(string fileName)
{
    _fileStream = File.Open(fileName, FileMode.Create, FileAccess.Write, FileShare.Read);
    _bufferedStream = new BufferedStream(_fileStream, APPENDBUFFERSIZE);
    _streamWriter = new StreamWriter(_bufferedStream);
}

public void Write(string data)
{
    _streamWriter.Write(data);
}

public void Close()
{
    if (_streamWriter != null)
    {
        _streamWriter.Flush();
        _streamWriter.Dispose();
        _streamWriter = null;
    }
    if (_bufferedStream != null)
    {
        _bufferedStream.Dispose();
        _bufferedStream = null;
    }
    if (_fileStream != null)
    {
        _fileStream.Dispose();
        _fileStream = null;
    }
}

Why doesn't the data get written to disk until I call Close? Technical data: I write 9000 KB worth of data

StreamWriter class has:

internal const int DefaultBufferSize = 1024;

FileStream class has:

internal const int DefaultBufferSize = 4096;

BufferedStream should be 65536 bytes. filename is a full path to a file on my local drive D.

filename = "D:\\Folder1\Folder2\\file.txt"

And I do have permissions to write to it. For a call to Write I use something similar to:

data = "1234567889|ababababababababbabababababababababababab"

Also, I don't want to get rid of the buffer, I just want the stream to be flushed every now and then, and see it on disk. It's weird to have the file to 0 KB and all of the sudden when you close, it's big. So by all measurements, all the buffers should overflow unless written to next stream/disk. Still, Windows only shows file size greater than 0 KB, after Close, although I've waited a few minutes after the writing to file has finished.

Any ideas?

Thanks, Ciprian.

UPDATE: The size appears 0 in windows explorer size column. If I look at file properties, then the size is larger than 0(which is correct). After I return from the properties window and refresh the windows explorer window, the size column gets updated to a value larger than 0. I I just refresh the windows explorer window without looking at file properties, the size column stays at 0. Also if I open the file with notepad++, it has all the data, and a refresh on the windows explorer window shows the correct value in the size column. So my issue is probably not due to the code I wrote, but you never know.

Upvotes: 1

Views: 231

Answers (2)

code4life
code4life

Reputation: 15794

Straight from the horse's mouth (aka MSDN):

Adds a buffering layer to read and write operations on another stream. This class cannot be inherited.

And further down in the remarks section:

A buffer is a block of bytes in memory used to cache data, thereby reducing the number of calls to the operating system

https://msdn.microsoft.com/en-us/library/system.io.bufferedstream(v=vs.110).aspx

So based on the documentation, your code is behaving as expected. Nothing will get written to disk unless one of 3 events occur:

  1. You Close() the buffered stream
  2. You Flush() it
  3. The buffer gets full

HTH...

Upvotes: 2

Xavier J
Xavier J

Reputation: 4724

You used a BufferedStream, which is not going to flush anything until you've reached 65536 bytes in the buffer, OR you call the Flush method, OR your call the Close method. If you want results sooner, take out the BufferedStream or change its size to a smaller number.

ONLY when the StreamWriter flushes (or closes), it writes to the BufferedStream, and ONLY when the BufferedStream flushes (or closes), it writes to the FileStream.

Additionally, the Windows (device) file buffer needs to do its magic AFTER .NET processing, and ultimately you have no control over when it actually persists data to the device.

Upvotes: 0

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