Articles → CSHARP → Nullable Datatypes

Nullable Datatypes

C# supports nullable data types. Nullable datatypes are those that contain the value of null.

int? i;

The above statement defines that "i" is the variable that allows nullable type Nullable version is a structure that combines value type with a flag to indicate whether the value is null or not.

Nullable types have 2 publicly read-only properties: -

HasValue → Set to true if there is a value stored, else false
Value → Get the value of variable

If "HasValue" is true then you can get the value of the variable else an exception will be thrown. Consider an example: -

int? i = null;
int j;
j = i;

This statement will throw an error as you cannot implicitly cast nullable type to a normal variable. To convert it, you must cast explicitly.

j = (int)i;

But you can cast implicitly int to int?

int? i;
int j = 5;
i = j;

Lifted Operators

Operators are also changed to allow the standard operators to work. These operators are called "lifted operators".

int? a = 3;
int b = 4;
int? c = a * b; // valid
int c = a * b; //invalid

Removing Nullability

?? operator is used for null coalescing.

int? i = null;
int j = 4;
int? c = i??j;

When you see the value of "c" it will come "4". This statement will first check the value of "I" if it is null then the value of "j" will be assigned to "c".

Posted By -	Karan Gupta

Posted On -	Friday, September 10, 2010

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