Which stream do I close when I do stream composition?

Question

If I have the following code:

FileStream fs = new FileStream(...);
TextWriter tw = new StreamWriter(fs);

Am I supposed to call only tw.Close(), or fs.Close() as well? I'm using the TextWriter persistently throughout an application, so I can't just wrap it in a Using(...) block, since I need to be able to use it at multiple points.

Otherwise, I would just write it as:

using (FileStream fs = new FileStream(...))
{
    using (TextWriter tw = new StreamWriter(fs))
    {
       // do stuff
    }
}

And avoid the issue at all together. But, I don't really know what to do in this circumstance. Do I close tw, fs, or both?

Also, more generally: If I compose multiple streams together, such as C(B(A)), can I call Close / Dispose on C and then not worry about having to call it on B and A?

Guffa · Accepted Answer · 2011-04-23T23:22:38.190

You only need to close the StreamWriter.

From the documentation of the StreamWriter.Close method:

Closes the current StreamWriter object and the underlying stream.

Also notable in the documentation of the method:

This implementation of Close calls the Dispose method passing a true value.

This means that closing and disposing the StreamWriter are equivalent. You don't have to dispose the object after closing it, or close it before disposing it. The FileStream.Close method does the same, so closing or disposing the StreamWriter will also dispose the stream.

If you wouldn't be able to find information like this for a class, you can always dispose both the writer and the stream to be safe. Disposing an object that has already been disposed does not cause any problem, and the method would just do nothing. Just make sure to close them in the right order, i.e. closing the writer before the stream.

score 1 · Answer 2 · edited May 23 '17 at 12:18

1

Because you have already enclosed your stream declaration in a "using" statement you to not need to specifically do either. Using invokes dispose and the dispose invokes close.

See this article from SO

edited May 23 '17 at 12:18

Community

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answered Apr 23 '11 at 23:17

Cos Callis

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That was not my question. I stated that if I could use the Using(...) idiom I would not need to do a Close or Dispose. – Mike Bailey Apr 23 '11 at 23:25
Indeed, I missed that part. Given that I would differ to @Guffa's answer. – Cos Callis Apr 23 '11 at 23:32

dahlbyk · Answer 3 · 2011-04-23T23:16:07.763

0

You're safe to Dispose() both tw and fs. If tw does happen to Dispose() the underlying stream, calling Dispose() again will be a no-op.

Update: Now I see the real question... In your case, I would turn to ILSpy which shows that TextWriter.Dispose() does indeed call Close() on the underlying stream. So you're fine to just call tw.Dispose().

edited Apr 23 '11 at 23:16

answered Apr 23 '11 at 23:09

dahlbyk

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Which stream do I close when I do stream composition?

3 Answers3