What is the difference between ref and out keyword in C#?

Question

Maha · Answer

Both are quite different. You can see in the following example. Even though MethodWithRefParam() is a void method (meaning that nothing is returned to the Main() method), when the program prints the variable for the second time within the Main() method, value has been changed to 888, Because variable (var) is passed by reference , the MethodWithRefParam() method "knows" the address of the variable declared in Main() , and makes its changes directly to the original variable that was declared in the Main() method. //Reference Parameter using System; public class ParameterDemo2 { public static void Main() { int var = 4; Console .WriteLine( "In Main var is {0}" , var); MethodWithRefParam( ref var); //calling method with a reference parameter Console .WriteLine( "In Main var is {0}" , var); Console .ReadKey(); } public static void MethodWithRefParam( ref int parm) { parm = 888; Console .WriteLine( "In MethodWithRefParam, param is {0}" , parm); } } /* In Main var is 4 In MethodWithRefParam, param is 888 In Main var is 888 */ When you use a reference parameter, the passed variable must have an assigned value. Using an output parameter is convenient when the passed variable doesn't have a value yet. For example, the program uses InputMethod() to obtain values for two parameters. The parameters get their values from the method, so it makes sense to provide them with no values going in, but to have them retain values coming out. using System; public class InputMethodDemo { public static void Main() { int first, second; InputMethod( out first, out second); // notice use of out Console .WriteLine( "After InputMethod first is {0} and second is {1}" , first, second); } // notice use of out public static void InputMethod( out int one, out int two) { string s1, s2; Console .Write( "Enter first integer " ); s1 = Console .ReadLine(); one = Convert .ToInt32(s1); Console .Write( "Enter second integer " ); s2 = Console .ReadLine(); two = Convert .ToInt32(s2); } } /* Enter first integer 2 Enter second integer 4 After InputMethod first is 2 and second is 4 */

Ranjit Powar · Answer

ref and out keyword will execute in same way. The only difference is you must initialize ref variable in the calling method before it is passed to called method. In case of out variable there is no need to initialization in calling method but in called method it must be initialize to value.

Jignesh Trivedi · Answer

Hi, Please refer my article http://www.c-sharpcorner.com/UploadFile/ff2f08/ref-vs-out-keywords-in-C-Sharp/ hope this will help you.

Vinitha T · Answer

Both are used to pass an method argument. Method arguments can passed by value, while calling method pass a data to called method, it modifies the data but won't visible in calling method. So, ref and out keyword is used to have visible changes in the calling method. Ref Keyword: ref keyword is used to pass a value to calling method and that value should be initialized before calling method. static void Main(string[] args){ int val=2; method1(ref val); Console.WriteLine(val); } public static void method1(ref int val){ val=4; } output : 4 Out Keyword: Here we should not initialize parameter before calling the method. static void Main(string[] args){ int val; method1(out val); Console.WriteLine(val); } static void method1(out ini val){ i=2; } output: 2 Main differences are : ref may or may not initialize a parameter in called method but out should initialize a parameter in called method. To return multiple values from method out could be used.

Upendra Pratap Shahi · Answer

http://www.dotnet-tricks.com/Tutorial/csharp/K0Hb060414-Difference-between-ref-and-out-parameters.html http://www.c-sharpcorner.com/UploadFile/ff2f08/ref-vs-out-keywords-in-C-Sharp/