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.NET Forum / Languages / C# / October 2006reference type
i understand that in csharp "string" and "object" are reference type... For e.g. in this case myString is passed to a method and it changes the value of the string.. if string is a reference type, isnt it passed to the method by reference and the second WriteLine should be "edited" instead of "hello world" ? String myString = "hello world"; Console.WriteLine("String before function : " + myString); doSomethingToString(myString); Console.WriteLine("String afer function : " + myString); static void doSomethingToString(string myString) { myString = "edited"; } It is a reference type passed by value; since you reassign the string this is behaving correctly. As always, Jon puts it better than I could: http://www.yoda.arachsys.com/csharp/parameters.html (sorry Jon, I always intend to use the pobox address, but google says yoda...) Marc In C# arguments are passed by value - thus only the copy myString in function scope is modified. If you want to modify an argument, you must use the 'ref' keyword to pass the argument by reference. For example > String myString = "hello world"; > [quoted text clipped - 6 lines] > myString = "edited"; > } will result in myString being modified in the main scope. GPG > i understand that in csharp "string" and "object" are reference type... > [quoted text clipped - 14 lines] > myString = "edited"; > } No, because with the statement myString = "edited"; you don't change the contents of the original string, but create a new string (containing "edited") and changing the reference of the local variable myString to point to that new string. When you return from that function, the original reference is still in place, so you see the original text. (Note: there are two separate 'myString' variables here: one 'global', the other local to the method) Hans Kesting > i understand that in csharp "string" and "object" are reference type... > > For e.g. in this case > myString is passed to a method and it changes the value of the string.. No, actually it doesn't change the value of the string. Strings are immutable in .NET, meaning that the value of the string object never changes. Instead a completely new string object is used and the reference to that object replaces the old reference. > if string is a reference type, isnt it passed to the method by > reference and the second WriteLine should be "edited" instead of "hello > world" ? No, all parameters are passed by value by default. For a reference type that means that the reference is passed by value, i.e. the value of the reference is copied. In the method you are using the copy of the reference, so eventhough you replace the reference with the reference to the new string, that does not change the original reference. Free MagazinesGet these publications absolutely FREE for up to 12 months. There are no hidden fees and no obligation. Simply choose a title, complete the application form and submit it. Read more ...
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