How to Box and Unbox Variables - C#

26 Apr. 2021 | Updated 14 May. 2021 | 1 min read.

Boxing and unboxing are important concepts in C#, allowing you to convert .NET data types from a value type to a reference type, and visa versa.

There are three data types in C#:

  • Value types - These include types such as int, char, and bool. A variable of a value type contains an instance of the type.
  • Reference types - These include types such as strings, arrays, and objects. A variable of a reference type contains a reference to the instance of the type.
  • Pointer types - A variable that holds the memory address of another type.

What is Boxing?

Boxing allows us to convert a value type, into a reference type:

class BoxingUnboxing
{  
    static void Main()  
    {  
        int myVal = 1;  
        object obj = myVal; // Boxing  
	}
}

Since we were able to assign directly to object without any special syntax, the conversion is implicit.

What is Unboxing?

Unboxing however, allows us to convert a reference type back into a value type:

class BoxingUnboxing
{  
    static void Main()  
    {  
        int myVal = 1;  
        object obj = myVal; // Boxing  
        int newVal = (int)obj; // Unboxing  
    }  
}

Unlike the boxing example, we needed to cast the object back using (int) before assigning it. This conversion is explicit.

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