C# 4 and .NET 4

156 ❘ ChaPTer 7 OperAtOrs And cAsts
This will display the number 4 , because an int is 4 bytes long.
If you are using the sizeof operator with complex types (and not primitive types), you will need to block
the code within an unsafe block as illustrated here:
unsafe
{
Console.WriteLine(sizeof(Customer));
}
Chapter 13 looks at unsafe code in more detail.
The typeof operator
The typeof operator returns a System.Type object representing a specifi ed type. For example,
typeof(string) will return a Type object representing the System.String type. This is useful when you
want to use refl ection to fi nd information about an object dynamically. Chapter 14, “ Refl ection, ” looks at
refl ection.
nullable Types and operators
Looking at the Boolean type, you have a true or false value that you can assign to this type. However, what
if you wanted to defi ne the value of the type as undefi ned This is where using nullable types can have a
distinct value to your applications. If you use nullable types in your programs, you must always consider
the effect a null value can have when used in conjunction with the various operators. Usually, when using a
unary or binary operator with nullable types, the result will be null if one or both of the operands is null .
For example:
int a = null;
int b = a + 4;
int c = a * 5;
// b = null
// c = null
However, when comparing nullable types, if only one of the operands is null , the comparison will always
equate to false . This means that you cannot assume a condition is true just because its opposite is false ,
as often happens in programs using non - nullable types. For example:
int a = null;
int b = -5;
if (a > = b)
Console.WriteLine("a > = b");
else
Console.WriteLine("a < b");
The possibility of a null value means that you cannot freely combine nullable and
non-nullable types in an expression. This is discussed in the “Type Conversions”
section later in this chapter.
The null Coalescing operator
The null coalescing operator ( ) provides a shorthand mechanism to cater to the possibility of null values
when working with nullable and reference types. The operator is placed between two operands — the fi rst
operand must be a nullable type or reference type, and the second operand must be of the same type as the
fi r s t or of a t y p e t h at i s i mpl ic it ly c onver t ible to t he t y p e of t he fi r s t op era nd . T he nu l l c oa le s c i ng op erator
evaluates as follows:
➤
➤
If the fi rst operand is not null , then the overall expression has the value of the fi rst operand.
If the fi rst operand is null , then the overall expression has the value of the second operand.
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