C# 4 and .NET 4

o p e r a t o r s ❘ 155
When you try to run this code, you will get an error message like this:
Unhandled Exception: System.OverflowException: Arithmetic operation resulted in an
overflow at Wrox.ProCSharp.Basics.OverflowTest.Main(String[] args)
You can enforce overfl ow checking for all unmarked code in your program by
specifying the /checked compiler option.
If you want to suppress overfl ow checking, you can mark the code as unchecked :
byte b = 255;
unchecked
{
b++;
}
Console.WriteLine(b.ToString());
In this case, no exception will be raised, but you will lose data — because the byte type cannot hold a value
of 256, the overfl owing bits will be discarded, and your b variable will hold a value of zero (0).
Note that unchecked is the default behavior. The only time you are likely to need to explicitly use the
unchecked keyword is if you need a few unchecked lines of code inside a larger block that you have
explicitly marked as checked .
The is operator
The is operator allows you to check whether an object is compatible with a specifi c type. The phrase
“ is compatible ” means that an object either is of that type or is derived from that type. For example, to
check whether a variable is compatible with the object type, you could use the following bit of code:
int i = 10;
if (i is object)
{
Console.WriteLine("i is an object");
}
int , like all C# data types, inherits from object ; therefore, the expression i is object will evaluate to
true in this case, and the appropriate message will be displayed.
The as operator
The as operator is used to perform explicit type conversions of reference types. If the type being converted
is compatible with the specifi ed type, conversion is performed successfully. However, if the types are
incompatible, the as operator returns the value null . As shown in the following code, attempting to convert
an object reference to a string will return null if the object reference does not actually refer to a
string instance:
object o1 = "Some String";
object o2 = 5;
string s1 = o1 as string; // s1 = "Some String"
string s2 = o2 as string; // s2 = null
The as operator allows you to perform a safe type conversion in a single step without the need to fi rst
test the type using the is operator and then perform the conversion.
The sizeof operator
You can determine the size (in bytes) required on the stack by a value type using the sizeof operator:
Console.WriteLine(sizeof(int));
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