Does 'using' still work right this way?

Question

1.60/5 (2 votes)

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.NET3.5

C#

private void SomeFunction()
{
    using (StreamReader sr = new StreamReader("C:\\File.txt"))
    {
        if (someCondition)
        {
            return;
        }
    }
}

Maybe a stupid question...
But does the file still get closed given that the return statement jumps out of the function?

Posted 27-Feb-13 9:57am

DanielSheets

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Comments

Richard C Bishop 27-Feb-13 15:59pm

Well, your function is not set to return anything, but I am not sure on the file getting closed. I think it is still good practice to manually close it.

Sergey Alexandrovich Kryukov 27-Feb-13 16:12pm

You should know such thing, as it is very important! Of course it will be closed (more exactly IDispoable.Dispose is automatically called) Please see my answer.
See also "using statement" on MDSN.
—SA

Sergey Alexandrovich Kryukov 27-Feb-13 16:16pm

By the way, OP could easily just check it up, with throwing exception and without it. It's a good idea to always try key techniques.
—SA

Richard C Bishop 27-Feb-13 17:25pm

Ok, I will take your advice, thank you.

Sergey Alexandrovich Kryukov 27-Feb-13 17:31pm

You are very welcome. I don't know if you saw the most recent version of my answer; I've added to it 3 times; but right now it's pretty much comprehensively explains everything.
—SA

3 solutions

Solution 3

Hi,
Yes,the file will be closed, and all the resources inside the using statement will be disposed regardless of what happens.

See microsoft article :
http://msdn.microsoft.com/en-gb/library/yh598w02.aspx[^]

Regards
Jegan

Posted 27-Feb-13 12:07pm

Jegan Thiyagesan

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This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

Sergey Alexandrovich Kryukov · Accepted Answer · 2013-02-27T10:07:00

Solution 1

Of course, it will work properly.

[EDIT]

The use of using is strictly equivalent to analogous try-finally statement with sr.Dispose() in the finally block. The using statement is just a syntax sugar (http://en.wikipedia.org/wiki/Syntax_sugar[^]).

C#

private void SomeFunction()
{
    StreamReader sr = new StreamReader("C:\\File.txt");
    try {
        if (someCondition)
            return;
    } finally {
       sr.Dispose(); // same happens "on the closing '}' of using statement"
    }
}

Please see: http://msdn.microsoft.com/en-us/library/yh598w02%28v=vs.80%29.aspx[^].

—SA

Posted 27-Feb-13 10:07am

Sergey Alexandrovich Kryukov

Updated 27-Feb-13 10:15am

v4

Comments

DanielSheets 27-Feb-13 18:07pm

Thanks! For some reason my mind is telling me that the closing brace is never reached because of the return statement.

Noobish... I know.

Sergey Alexandrovich Kryukov 27-Feb-13 18:11pm

You are welcome.
And it's perfectly all right: if you are in doubt, you should always check up things, I appreciate it. Only you could easily check it by yourself; in future, please always try by yourself first.
Good luck, call again.
—SA

Sergey Alexandrovich Kryukov 27-Feb-13 18:14pm

As to "never reached"... this is a typical confusion of try-finally, exceptions in general and "using" statement. Look at it this way: '}' is not a statement, if cannot be "reached". It's only end of context, not a sequence of any CPU or CIL instructions. If you look at decompiled code, you won't see any instructions associated to '}'. If you look this way, some weirdness you might see right now should disappear.
—SA

DanielSheets 27-Feb-13 18:25pm

Great explanation! And you're right... I never thought of it that way. That does take some of the mud out of the water.

Sergey Alexandrovich Kryukov 27-Feb-13 18:29pm

I hope so. Thank you, Daniel.
Good luck,
—SA

CCPFC · Accepted Answer · 2013-02-27T10:10:00

Solution 2

Yes. Use ILdasm to examine the IL produced. Hint: a 'finally' clause is generated that includes the code to Dispose() of your reader.

Posted 27-Feb-13 10:10am

CCPFC

Does 'using' still work right this way?

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