Difference between out and ref keyword in C#

out keyword

out keyword is used to pass arguments to method as a reference type and is primary used when a method has to return multiple values. ref keyword is also used to pass arguments to method as reference type and is used when existing variable is to be modified in a method. Following is the valid usage of ref and out keywords in C#.

Example

 Live Demo

using System.IO;
using System;
public class Program {
   public static void update(out int a){
      a = 10;
   }
   public static void change(ref int d){
      d = 11;
   }
   public static void Main() {
      int b;
      int c = 9;
      Program p1 = new Program();
      update(out b);
      change(ref c);
      Console.WriteLine("Updated value is: {0}", b);
      Console.WriteLine("Changed value is: {0}", c);
   }
}

Output

Updated value is: 10
Changed value is: 11

Following are some of the important differences between ref and out keywords.

Sr. No.	Key	ref keyword	out keyword
1	Purpose	ref keyword is used when a called method has to update the passed parameter.	out keyword is used when a called method has to update multiple parameter passed.
2	Direction	ref keyword is used to pass data in bi-directional way.	out keyword is used to get data in uni-directional way.
3	Initialization	Before passing a variable as ref, it is required to be initialized otherwise compiler will throw error.	No need to initialize variable if out keyword is used.
4	Initialization	In called method, it is not required to initialize the parameter passed as ref.	In called method, it is required to initialize the parameter passed as out.