using statement - C# Reference
using statement (C# Reference)
Provides a convenient syntax that ensures the correct use of xref:System.IDisposable objects.
The following example shows how to use the
xref:System.IO.File and xref:System.Drawing.Font are examples of managed types that access unmanaged resources (in this case file handles and device contexts). There are many other kinds of unmanaged resources and class library types that encapsulate them. All such types must implement the xref:System.IDisposable interface.
When the lifetime of an
IDisposable object is limited to a single method, you should declare and instantiate it in the
using statement. The
using statement calls the xref:System.IDisposable.Dispose%2A method on the object in the correct way, and (when you use it as shown earlier) it also causes the object itself to go out of scope as soon as xref:System.IDisposable.Dispose%2A is called. Within the
using block, the object is read-only and cannot be modified or reassigned.
using statement ensures that xref:System.IDisposable.Dispose%2A is called even if an exception occurs within the
using block. You can achieve the same result by putting the object inside a
try block and then calling xref:System.IDisposable.Dispose%2A in a
finally block; in fact, this is how the
using statement is translated by the compiler. The code example earlier expands to the following code at compile time (note the extra curly braces to create the limited scope for the object):
For more information about the
finally statement, see the try-finally topic.
Multiple instances of a type can be declared in the
using statement, as shown in the following example:
You can instantiate the resource object and then pass the variable to the
using statement, but this is not a best practice. In this case, after control leaves the
using block, the object remains in scope but probably has no access to its unmanaged resources. In other words, it's not fully initialized anymore. If you try to use the object outside the
using block, you risk causing an exception to be thrown. For this reason, it's generally better to instantiate the object in the
using statement and limit its scope to the
For more information about disposing of
IDisposable objects, see Using objects that implement IDisposable.