What is the C# Using block and why should I use it

Question

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• What are the uses of “using” in C# 29 answers

What is the purpose of the Using block in C#? How is it different from a local variable?

Answer 1

Using calls Dispose() after the using-block is left, even if the code throws an exception.

So you usually use using for classes that require cleaning up after them, like IO.

So, this using block:

using (MyClass mine = new MyClass())
{
  mine.Action();
}

would do the same as:

MyClass mine = new MyClass();
try
{
  mine.Action();
}
finally
{
  if (mine != null)
    mine.Dispose();
}

Using using is way shorter and easier to read.

Answer 2

It is really just some syntatic sugar that does not require you to explicity call Dispose on members that implement IDisposable.

Answer 3

Placing code in a using block ensures that the objects are disposed (though not necessarily collected) as soon as control leaves the block.

Answer 4

using (B a = new B())
{
   DoSomethingWith(a);
}

is equivalent to

B a = new B();
try
{
  DoSomethingWith(a);
}
finally
{
   ((IDisposable)a).Dispose();
}

Answer 5

The using statement obtains one or more resources, executes a statement, and then disposes of the resource.

Answer 6

Also take note that the object instantiated via using is read-only within the using block. Refer to the official C# reference here.