Writing to txt file with StreamWriter and FileStream

Question

I ran into something interesting when using a StreamWriter with a FileStream to append text to an existing file in .NET 4.5 (haven't tried any older frameworks). I tried two ways, one worked and one didn't. I'm wondering what the difference between the two is.

Both methods contained the following code at the top

if (!File.Exists(filepath))     using (File.Create(filepath)); 

I have the creation in a using statement because I've found through personal experience that it's the best way to ensure that the application fully closes the file.

Non-Working Method:

using (FileStream f = new FileStream(filepath, FileMode.Append,FileAccess.Write))     (new StreamWriter(f)).WriteLine("somestring"); 

With this method nothing ends up being appended to the file.

Working Method:

using (FileStream f = new FileStream(filepath, FileMode.Append,FileAccess.Write))     using (StreamWriter s = new StreamWriter(f))         s.WriteLine("somestring"); 

I've done a bit of Googling, without quite knowing what to search for, and haven't found anything informative. So, why is it that the anonymous StreamWriter fails where the (non-anonymous? named?) StreamWriter works?

Answer 1

It sounds like you did not flush the stream.

http://msdn.microsoft.com/en-us/library/system.io.stream.flush.aspx

It looks like StreamWriter writes to a buffer before writing to the final destination, in this case, the file. You may also be able to set the AutoFlush property and not have to explicitly flush it.

http://msdn.microsoft.com/en-us/library/system.io.streamwriter.autoflush.aspx

To answer your question, when you use the "using" block, it calls dispose on the StreamWriter, which must in turn call Flush.

Answer 2

The difference between the two code snippets is the use of using. The using statement disposes the object at the end of the block.

A StreamWriter buffers data before writing it to the underlying stream. Disposing the StreamWriter flushes the buffer. If you don't flush the buffer, nothing gets written.

From MSDN:

You must call Close to ensure that all data is correctly written out to the underlying stream.

See also: When should I use “using” blocks in C#?