ECMA-334 C# Language Specification

14.5.11: The typeof operator

The typeof operator is used to obtain the System.Type object for a type.

typeof-expression
typeof ( type )
typeof (void )

The first form of typeof-expression consists of a typeof keyword followed by a parenthesized type. The result of an expression of this form is the System.Type object for the indicated type. There is only one System.Type object for any given type. [Note: This means that for type T, typeof(T) == typeof(T) is always true. end note]

The second form of typeof-expression consists of a typeof keyword followed by a parenthesized void keyword. The result of an expression of this form is the System.Type object that represents the absence of a type. The type object returned by typeof(void ) is distinct from the type object returned for any type.

[Note: This special type object is useful in class libraries that allow reflection onto methods in the language, where those methods wish to have a way to represent the return type of any method, including void methods, with an instance of System.Type. end note]

[Example: The example 
using System;  
class Test  
{  
   static void Main() {  
      Type[] t = {  
         typeof(int),  
         typeof(System.Int32),  
         typeof(string),  
         typeof(double[]),  
      typeof(void)   };  
      for (int i = 0; i < t.Length; i++) {  
         Console.WriteLine(t[i].FullName);  
      }  
   }  
}
produces the following output: 
System.Int32  
System.Int32  
System.String  
System.Double[]  
System.Void

Note that int and System.Int32 are the same type. end example]