confused when using "using block" - C#

Question

I often use the "using" block to dispose the objects. Today, I using HttpWebRequest to post data, and I feel confused between two method.

Method 1:

var request = (HttpWebRequest)WebRequest.Create("http://www...");
using (var writer = new StreamWriter(request.GetRequestStream()))
{
    writer.Write(JsonConvert.SerializeObject(content));
}

Method 2:

var request = (HttpWebRequest)WebRequest.Create("http://www...");
using (var stream = request.GetRequestStream())
using (var writer = new StreamWriter(stream))
{
    writer.Write(JsonConvert.SerializeObject(content));
}

In method 2, all stream and streamwirter in "using" blocks, so certainly it will be dispose. But in method 1, I am not sure stream request.GetRequestStream() will be dispose. Can anyone explain to me? Thanks alot!

Jon Skeet · Accepted Answer · 2016-05-06 17:42:53Z

9

Basically, it depends on two things:

Whether the StreamWriter constructor will ever throw an exception when passed a non-null Stream reference - and I don't think it will in this case. (If the stream were read-only, it would... at which point the stream wouldn't be disposed.)
Whether StreamWriter.Dispose disposes of the underlying stream - and it does, unless you've called the constructor overload which explicitly allows you to control that

So basically, I believe it's safe in this case... when your using statement disposes of the StreamWriter, that will dispose of the Stream.

As noted in comments, however, using two using statements means you don't need to perform this sort of reasoning.

edited May 6, 2016 at 17:42

answered May 6, 2016 at 16:46

Jon Skeet

1.5m893 gold badges9.3k silver badges9.3k bronze badges

Sign up to request clarification or add additional context in comments.

4 Comments

Minh Giang Over a year ago

So, method 1 is as safe as method 2?

Jon Skeet Over a year ago

@MinhGiang: Yes, exactly.

tlt Over a year ago

Are you sure about that? If Stream.CanWrite is false for whatever reason (something unpredictable happens with request) then StreamWriter constructor will throw ArgumentException and underlying stream might end up not being disposed. Not saying its likely to happen but want to point out that some practices (like method 1) force you to think about particular implementations (which also might change in future, of course) and some practices don't. That's the reason why i would personally always choose method 2.

Jon Skeet Over a year ago

@deezg: That's a good point; I think it's okay in this case but I'll update the post.

adv12 · Accepted Answer · 2016-05-06 16:46:38Z

5

A StreamWriter wrapping a Stream will close that stream when it is closed. See the docs.

answered May 6, 2016 at 16:46

adv12

8,5512 gold badges28 silver badges52 bronze badges

Comments

taquion · Accepted Answer · 2016-05-06 16:49:24Z

-2

Both are the same. Since using block disposes the entire object, even anonymous objects.

answered May 6, 2016 at 16:49

taquion

2,7972 gold badges20 silver badges33 bronze badges

2 Comments

Jon Skeet Over a year ago

No, they're not the same. The using statement only calls Dispose on the resources specified in the first part - this code is only okay because StreamWriter calls Dispose on the Stream that's passed into the constructor.

taquion Over a year ago

That seems to be true. I have read msdn.microsoft.com/es-es/library/…. Thank you

Collectives™ on Stack Overflow

confused when using "using block" - C#

3 Answers 3

4 Comments

Comments

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

4 Comments

Comments

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related