Typeof

The C# typeof operator returns Type objects. It is often used as a parameter or as a variable or field. It is part of an expression that acquires the Type pointer.

Some methods, like Enum.Parse, require a Type object, and typeof can get us this object. We use the typeof operator to get more information about a class.

Typeof example

Here we use typeof in a simple program. The types the program uses are found in the System namespace and the System.IO namespace.

using System;
using System.IO;

class Program
{
    static Type _type = typeof(char); // Store Type as field.

    static void Main()
    {
        Console.WriteLine(_type); // Value type pointer
        Console.WriteLine(typeof(int)); // Value type
        Console.WriteLine(typeof(byte)); // Value type
        Console.WriteLine(typeof(Stream)); // Class type
        Console.WriteLine(typeof(TextWriter)); // Class type
        Console.WriteLine(typeof(Array)); // Class type
        Console.WriteLine(typeof(int[])); // Array reference type
    }
}
System.Char
System.Int32
System.Byte
System.IO.Stream
System.IO.TextWriter
System.Array
System.Int32[]

Enum example

Some common uses of the typeof operator are the Enum static methods, the DataTable class and similar classes, and the ArrayList conversion methods.

using System;

enum AnimalType
{
    Bird
}

class Program
{
    public static void Main()
    {
        string name = "Bird";
        // Use Enum.Parse with typeof argument.
        var result = Enum.Parse(typeof(AnimalType), name);
        // Test result.
        if ((AnimalType)result == AnimalType.Bird)
        {
            Console.WriteLine("OK");
        }
    }
}
OK

Summary

Typeof is an operator. We assigned the result of typeof expressions to a Type field or variable. There are many common uses of the typeof operator in .NET.