typeof Operator Keyword in C#

The typeof is an operator keyword which is used to get a type at the compile-time. Or in other words, this operator is used to get the System.Type object for a type. This operator takes the Type itself as an argument and returns the marked type of the argument.

Important points:

  • The operand of typeof operator is always a type of parameter or name of the type. It does not contain variable.
  • It is not allowed to overload typeof operator.
  • It is allowed to use typeof operator on open generic types.
  • It is allowed to use typeof operator on bounded or unbounded types.

Syntax:



System.Type type = typeof(int);

Here, type is the type that is obtained.

Example :

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// C# program to illustrate the
// concept of typeof operator
using System;
  
class GFG {
  
    // Here store Type as a field
    static Type a = typeof(double);
  
    // Main method
    static void Main()
    {
  
        // Display the type of a
        Console.WriteLine(a);
  
        // Display the value type
        Console.WriteLine(typeof(int));
  
        // Display the class type
        Console.WriteLine(typeof(Array));
  
        // Display the value type
        Console.WriteLine(typeof(char));
  
        // Display the array reference type
        Console.WriteLine(typeof(int[]));
    }
}

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Output:

System.Double
System.Int32
System.Array
System.Char
System.Int32[]

Difference between typeof operator and GetType method

typeof Operator GetType Method
It takes the Type itself as an argument and returns the marked type of the argument. It only invoked on the instance of the type.
It is used to get a type that is known at compile-time. It is used to obtain the type of an object at run-time.
It cannot be used on an instance. It can be used on instance.

Example:

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// C# program to illustrate the
// difference between typeof 
// operator and GetType method
using System;
  
public class GFG {
  
    // Main method
    static public void Main()
    {
        string s = "Geeks";
  
        // using typeof opertor
        Type a1 = typeof(string);
  
        // using GetType method
        Type a2 = s.GetType();
  
        // checking for equality
        Console.WriteLine(a1 == a2);
  
        // taking a type object
        object obj = "Hello";
  
        // using typeof operator
        Type b1 = typeof(object);
  
        // using GetType method
        Type b2 = obj.GetType();
  
        // checking for equality
        // it will return False as 
        // GetType method is used 
        // to obtain run-time type
        Console.WriteLine(b1 == b2);
    }
}

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Output:

True
False

Explanation: Here, Type b1 = typeof(object); this will return System.Object but Type b2 = obj.GetType(); will return System.String. As, at compile time only object type reference is created, but at runtime the string(“Hello”) is actually storing in it.



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