What is boxing and unboxing in C#?

In C#, the concepts of boxing and unboxing hold immense significance as they provide a unified typeType of value that a variable holds system for programmers to manipulate and treat each variable as an object.

There are three types in C# for a variable:

  • Value type: This deals with variables that hold values of int, char, float, and so on.

  • Reference type: This deals with objects in C#.

  • Pointer type: This deals with the addresses of variables/objects.

Boxing deals with converting a value type to a reference type, while unboxing deals with converting a reference type to a value type.

Example

Let's take an example for each concept and see how programmers use them to code efficiently.

Boxing

We will implement the implicit conversionThis is the conversion of a derived class object to a base class object. of a value type to a reference type via boxing:

using System;
class HelloWorld
{
    static void Main()
    {
        char valVariable = 'H';
        object refVariable;
        //boxing
        refVariable = valVariable;
        valVariable = 'A';
        Console.WriteLine("Value of valVariable: {0}",valVariable);
        Console.WriteLine("Value of refVariable: {0}",refVariable);
    }
}

Explanation

  • Line 6: We declare and initialize the variable of a value type.

  • Lines 7–9: We declare the variable of the reference type with object, and boxing occurs when it is initialized with the value type variable's value.

  • Lines 11–12: We print the output of both types to display how boxing changes the reference type variable's value to a value type. Even when we change the valVariable's value, it does not reflect those changes in the refVariable.

Unboxing

The code below shows the implementation of the concept of unboxing:

using System;
class HelloWorld
{
    static void Main()
    {
        int valVariable = 10;
        //boxing
        object refVariable = valVariable;
        //unboxing
        int valVariable2 = (int)refVariable;
        Console.WriteLine("Value of refVariable:{0}",refVariable);
        Console.WriteLine("Value of valVariable2:{0}",valVariable2);
    }
}
Explanation

  • Line 6: We initialize the value type variable.

  • Line 8: We initialize the reference type variable with the value type variable's value.

  • Line 10: We initialize another value type variable with the reference type variable's value. Unboxing is the concept where explicit conversionThis is the conversion of a base class object to a derived class object. occurs. Here, (int) represents this conversion.

  • Lines 11–12: We print the output of the refVariable and the valVariable to show how we can use unboxing to assign a reference type variable's value to a value type variable.

Differences

The following table represents the differences between the two concepts:

Boxing

Unboxing

Conversion of value type to reference type.

Conversion of reference type to value type.

Stack variable's value given to an object stored on heap.

Heap object's value given to a variable stored on the stack.

Implicit conversion.

Explicit conversion.

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