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Use Using!

, 8 Oct 2010
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The c# using syntax is often overlooked
This is probably an obvious tip to most seasoned C# developers, but I often come across people posting code that doesn't handle cleanup properly in the event of an error. (or not at all!)
 
Any object that implements IDisposable can be wrapped with a using statement as follows:
using(IDisposable x = ...)
{
   // do something with x
}
 
The using statement guarantees that the object will be disposed, even if something goes wrong or if the scope is otherwise exited.
 
A sample mistake is something like this (simplified for demonstration, this is NOT good code!)
 
public string ReadHtml(string url) {
        System.Net.HttpWebRequest wr = (System.Net.HttpWebRequest)WebRequest.Create(url);
        System.Net.HttpWebResponse resp = (System.Net.HttpWebResponse)wr.GetResponse();
 
        System.IO.StreamReader sr = new System.IO.StreamReader(resp.GetResponseStream());
        return sr.ReadToEnd();
}
 
Now, because this is such a simple demo, you and I can see that the return statement happens before the stream is closed, but when conditional logic is used, this can be much less obvious.
 
If, instead, this code was written as
 
public string ReadHtml(string url) {
        System.Net.HttpWebRequest wr = (System.Net.HttpWebRequest)WebRequest.Create(url);
        System.Net.HttpWebResponse resp = (System.Net.HttpWebResponse)wr.GetResponse();
 
        using(System.IO.StreamReader sr = new System.IO.StreamReader(resp.GetResponseStream())) {
            return sr.ReadToEnd();
       }
}
 
then the stream would be properly disposed.
 
It's an easy syntax to use and can avoid performance problems when your code goes into production.
 
Note:
using(...) {} is functionally equivalent to
IDisposable x = ...;
try {
 
} finally { x.Dispose(); }

License

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

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About the Author

Nathan Staudt
Web Developer
United Kingdom United Kingdom
I've been a web application developer since the late 1990s, working for eCommerce, media and telecoms companies across europe and america.
 
I have a BSc (Hons) in computing from Middlesex University and took a few MCP exams several years ago too.
 
Born in America, I grew up in Ireland. My father encouraged my interest in computers as a child when he would bring home his "portable" ibm pc... (20kg or something like that) and I first wrote some stuff in QBasic aged seven or eight, but my real interest in computers took off when my family got internet access at home in the early 90s.
 
Feel free to email me Smile | :)

Comments and Discussions

 
GeneralThis is just being picky, but the final note is not quite tr... PinmvpOriginalGriff27-Dec-11 1:00 
This is just being picky, but the final note is not quite true: the using block also causes the IDisposable object to go out of scope, which the try...finally block does not. It is legal (but very stupid) to write:
IDisposable x = ...;
try
{
...
}
finally { x.Dispose(); }
x.Read();
Which you cannot do with the equivalent using block.
Still gets a five though Smile | :)

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