Description
C# Nullable types can be applied to stand for all the values of an underlying type, including an additional null value. The Nullable types are instances of System.Nullable<T> which is a struct. A nullable type can be declared as a System.Nullable<T> variable or T? variable. T is the underlying type of the nullable type. T can be any value type, including struct, but it cannot be a reference type.
The main use of nullable types arises when dealing with databases and other data types that control elements with unassigned values. (For illustration, when the values returned from a table is NULL). Any value from -2,147,483,648 to 2,147,483,647 or null can be stashed away in a Nullable<Int32> variable. Likewise, one can assign true, false, or null in a Nullable<bool> variable. More
Syntax
The syntax for declaring a nullable type is as follows:
< data_type> ? <variable_name> = null; Example
[csharp]
using System;
using System.Collections.Generic;
using System.IO;
using System.Collections;
namespace SPLessons
{
class Program
{
static void Main(string[] args)
{
int? value = null;
Console.WriteLine(value.HasValue);
value = 10;
Console.WriteLine(value.HasValue);
Console.WriteLine(value.Value);
Console.WriteLine(value);
if (value == 1)
{
Console.WriteLine("True");
}
}
}
}
[/csharp]
Output:
Properties
The HasValue property returns a bool that indicates whether the instance has a value. If the type is null, it does not have a value and HasValue property is false. If the type is assigned to an integer, HasValue is true.