Export (0) Print
Expand All

Boxing Conversion

Visual Studio .NET 2003

Boxing is an implicit conversion of a value type to the type object or to any interface type implemented by this value type. Boxing a value of a value allocates an object instance and copies the value into the new object.

Consider the following declaration of a value-type variable:

int i = 123;

The following statement implicitly applies the boxing operation on the variable i:

object o = i;

The result of this statement is creating an object o, on the stack, that references a value of the type int, on the heap. This value is a copy of the value-type value assigned to the variable i. The difference between the two variables, i and o, is illustrated in the following figure.

Boxing Conversion

It also possible, but never needed, to perform the boxing explicitly as in the following example:

int i = 123;
object o = (object) i;

Example

This example converts an integer variable i to an object o via boxing. Then the value stored in the variable i is changed from 123 to 456. The example shows that the object keeps the original copy of the contents, 123.

// boxing.cs
// Boxing an integer variable
using System;
class TestBoxing  
{
   public static void Main() 
   {
      int i = 123;
      object o = i;  // Implicit boxing
      i = 456;       // Change the contents of i
      Console.WriteLine("The value-type value = {0}", i);
      Console.WriteLine("The object-type value = {0}", o);
   }
}

Output

The value-type value = 456
The object-type value = 123

See Also

Boxing and Unboxing | Unboxing Conversion

Show:
© 2014 Microsoft