C# 0 The Complete Reference

PART I

C h a p t e r   2 0 :  

U n s a f e   C o d e ,   P o i n t e r s ,   N u l l a b l e   T y p e s ,   a n d   M i s c e l l a n e o u s   T o p i c s  

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PART IPART I

    if(result.HasValue)

      Console.WriteLine("result has this value: " + result.Value);

    else

      Console.WriteLine("result has no value");

  }

}

The output is shown here:

result has no value

result has this value: 110

The ?? Operator

If you attempt to use a cast to convert a nullable object to its underlying type, a 

System.InvalidOperationException

 will be thrown if the nullable object contains a 

null

value. This can occur, for example, when you use a cast to assign the value of a nullable 

object to a variable of its underlying type. You can avoid the possibility of this exception 

being thrown by using the 

??

 operator, which is called the 

null coalescing operator

. It lets you 

specify a default value that will be used when the nullable object contains 

null

. It also 

eliminates the need for the cast.

The

??

 operator has this general form:

nullable-object

 ?? 

default-value

If

nullable-object

contains a value, then the value of the 

??

 is that value. Otherwise, the value 

of the 

??

 operation is 

default-value

.

For example, in the following code