Boxing and Unboxing

• 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 :
• // 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