as (C# Reference)

The as operator is used to perform certain types of conversions between compatible reference or nullable types. For example:

   class csrefKeywordsOperators
       class Base
           public override string  ToString()
                 return "Base";
       class Derived : Base 
       { }

       class Program
           static void Main()

               Derived d = new Derived();

               Base b = d as Base;
               if (b != null)



The as operator is like a cast operation. However, if the conversion is not possible, as returns null instead of raising an exception. Consider the following expression:

expression as type

It is equivalent to the following expression except that expression is evaluated only one time.

expression is type ? (type)expression : (type)null

Note that the as operator only performs conversions to reference or nullable types, and boxing conversions. The as operator cannot perform other conversions, such as user-defined conversions, which should instead be performed by using cast expressions.


class ClassA { }
class ClassB { }

class MainClass
    static void Main()
        object[] objArray = new object[6];
        objArray[0] = new ClassA();
        objArray[1] = new ClassB();
        objArray[2] = "hello";
        objArray[3] = 123;
        objArray[4] = 123.4;
        objArray[5] = null;

        for (int i = 0; i < objArray.Length; ++i)
            string s = objArray[i] as string;
            Console.Write("{0}:", i);
            if (s != null)
                Console.WriteLine("'" + s + "'");
                Console.WriteLine("not a string");
0:not a string
1:not a string
3:not a string
4:not a string
5:not a string

C# Language Specification

For more information, see the C# Language Specification. The language specification is the definitive source for C# syntax and usage.

See Also


C# Keywords

is (C# Reference)

?: Operator (C# Reference)

Operator Keywords (C# Reference)


C# Programming Guide

Other Resources

C# Reference