== Operator (C# Reference)

 

Updated: July 20, 2015

For predefined value types, the equality operator (==) returns true if the values of its operands are equal, false otherwise. For reference types other than string, == returns true if its two operands refer to the same object. For the string type, == compares the values of the strings.

User-defined value types can overload the == operator (see operator). So can user-defined reference types, although by default == behaves as described above for both predefined and user-defined reference types. If == is overloaded, != must also be overloaded. Operations on integral types are generally allowed on enumeration.

    class Equality
    {
        static void Main()
        {
            // Numeric equality: True
            Console.WriteLine((2 + 2) == 4);

            // Reference equality: different objects, 
            // same boxed value: False.
            object s = 1;
            object t = 1;
            Console.WriteLine(s == t);

            // Define some strings:
            string a = "hello";
            string b = String.Copy(a);
            string c = "hello";

            // Compare string values of a constant and an instance: True
            Console.WriteLine(a == b);

            // Compare string references; 
            // a is a constant but b is an instance: False.
            Console.WriteLine((object)a == (object)b);

            // Compare string references, both constants 
            // have the same value, so string interning
            // points to same reference: True.
            Console.WriteLine((object)a == (object)c);
        }
    }
    /*
    Output:
    True
    False
    True
    False
    True
    */

C# Reference
C# Programming Guide
C# Operators

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