Question

What is the difference in functionality between StreamWriter.Flush() and StreamWriter.Close()?

When my data wasn’t being written correctly to a file, I added both Flush() and Close() to the end of my code. However, I realized that adding either Flush() or Close() allowed the data to be written correctly.

I wasn’t able to pick up on exactly what each of these methods does when I read the MSDN docs; I only figured out that one or the other is necessary to ensure data is written correctly. Any further explanation would be much appreciated.

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Where s is a string to be written, here’s what my code looks like currently:

StreamWriter sw = File.CreateText("TextOutput.txt");
sw.Write(s);
sw.Flush();
sw.Close();

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Based on feedback from the answers, I’ve rewritten my code in a using block, which implements IDisposable and will automatically take care of writing the stream to the file when the object is disposed:

using (StreamWriter sw = File.CreateText("TextOutput.txt"))
{
    sw.Write(s);
}

Answer 1

StreamWriter.Flush() can be called any time you need to clear the buffer, and the stream will remain open.

StreamWriter.Close() is for closing the stream, at which point the buffer is also flushed.

But you shouldn’t really need to call either of these. Any time I see a .Close() in code I take that as a code smell, because it usually means an unexpected exception could cause the resource to be left open. What you should do, is create your StreamWriter variable in a using block, like this:

using (var writer = new StreamWriter("somefilepath.txt"))
{
   // write a bunch of stuff here
} // the streamwriter WILL be closed and flushed here, even if an exception is thrown.