Nullable in C#

 

Nullable Types:

 

v A value type cannot be assigned a null value. For example, int i = null will give you a compile time error.

 

v C# 2.0 introduced nullable types that allow you to assign null to value type variables.

 

v The Nullable type allows you to assign a null value to a variable. Nullable types can only work with Value Type, not with Reference Type.

 

v In nullable of integer type you can store values from -2147483648 to 2147483647, or null value.

 

v Nullable types do not support var type. If you use Nullable with var, then the compiler will give you a compile-time error.

 

v The main use of nullable type is in database applications. Suppose, in a table a column required null values, then you can use nullable type to enter null values.

 

v Nested Nullable types are not allowed. Nullable<Nullable<int>> i; will give a compile time error. 

Syntax:

1.   Nullable<data_type> variable_name = null;

 

2.   datatype? variable_name = null;

 

Example:

// this will give compile time error

int j = null;

 

// Valid declaration

Nullable<int> j = null;

 

// Valid declaration

int? j = null;

double? d = null;

 

Access Nullable Value:

v We cannot directly access the value of the Nullable type. Either we have to use .value or GetValueOrDefault() method.

 

v Nullable.value gives runtime error if value is null.

 

v GetValueOrDefault() method to get an original assigned value if it is not null.

 

v You will get the default value if it is null. The default value for null will be zero.

 

Nullable.HasValue:

v If the object assigned with a value, then it will return “True”.

 

v If the object is assigned to null, then it will return “False”

v If the object is not assigned with any value then it will give compile-time error.

 

null coalescing operator (?? Operator):

v Use the '??' operator to assign a nullable type to a non-nullable type.

 

v C# 2.0 introduced the?? Or null coalescing operator. The?? operator has two operands and can be used in an expression as follows:

 

x = y?? z;

 

v The?? operator returns the left-hand operand if the left-hand operand is not null, otherwise it returns the right-hand operand. In the example above, if ‘y’ is not null, then ‘x’ is set to ‘y’; however, if ‘y’ is null, then ‘x’ is set to ‘z’.