Prerequisite : Data Types in C#

Boxing and unboxing is an important concept in C#. C# Type System contains three data types: Value Types (int, char, etc), Reference Types (object) and Pointer Types. Basically it convert a Value Type to a Reference Type, and vice versa. Boxing and Unboxing enables a unified view of the type system in which a value of any type can be treated as an object.

Boxing In C#

• The process of Converting a Value Type (char, int etc.) to a Reference Type(object) is called Boxing.
• Boxing is implicit conversion process in which object type (super type) is used.
• The Value type is always stored in Stack. The Referenced Type is stored in Heap.
• Example :

  int num = 23; // 23 will assigned to num
  Object Obj = num; // Boxing
  

• Description : First declare a value type variable (num), which is integer type and assigned it with value 23. Now create a references object type (obj) and applied Explicit operation which results in num value type to be copied and stored in object reference type obj as shown in below figure :

  

• Let’s understand Boxing with a C# programming code :

  
  

  
  
  

  // C# implementation to demonstrate // the Boxing using System; class GFG {        // Main Method     static public void Main()     {            // assigned int value         // 2020 to num         int num = 2020;            // boxing         object obj = num;            // value of num to be change         num = 100;            System.Console.WriteLine         ("Value - type value of num is : {0}", num);         System.Console.WriteLine         ("Object - type value of obj is : {0}", obj);     } }

  Output:

  Value - type value of num is : 100
  Object - type value of obj is : 2020
  

Unboxing In C#

• The process of converting reference type into the value type is known as Unboxing.
• It is explicit conversion process.
• Example :

  int num = 23;         // value type is int and assigned value 23
  Object Obj = num;    // Boxing
  int i = (int)Obj;    // Unboxing
  

• Description : Declaration a value type variable (num), which is integer type and assigned with integer value 23. Now, create a reference object type (obj).The explicit operation for boxing create an value type integer i and applied casting method. Then the referenced type residing on Heap is copy to stack as shown in below figure :

  

• Let’s understand Unboxing with a C# programming code :

  
  

  
  
  

  // C# implementation to demonstrate // the Unboxing using System; class GFG {        // Main Method     static public void Main()     {            // assigned int value         // 23 to num         int num = 23;            // boxing         object obj = num;            // unboxing         int i = (int)obj;            // Display result         Console.WriteLine("Value of ob object is : " + obj);         Console.WriteLine("Value of i is : " + i);     } }

  Output:

  Value of ob object is : 23
  Value of i is : 23