About string ,and help me to solution one problom about zhe value and reference type! Thank you！ [modified]

[gjllyl]

hi, zhe subject is that class Class1 { private string str = "class1.str"; private int i = 0; static void StringConvert(string str) { str = "string being converted."; } static void StringConvert(Class1 c) { c.str = "string being converted."; } static void Add(int i) { i++; } static void AddWithRef(ref int i) { i++; } static void Main() { int i1 = 10; int i2 = 20; string str = "str"; Class1 c = new Class1(); Add(i1); AddWithRef(ref i2); Add(c.i); StringConvert(str); StringConvert(c); Console.WriteLine(i1); Console.WriteLine(i2); Console.WriteLine(c.i); Console.WriteLine(str); Console.WriteLine(c.str); Console.Read(); } tell me why "Console.WriteLine(str);" and "Console.WriteLine(c.str);" zhe two sentence have two different results! I know that zhe "string" is reference type! but here i am puzzled!

modified on Saturday, June 20, 2009 8:09 AM

[Gideon Engelberth]

While you are correct that string is a reference type, you cannot change which string the local variable str in Main is referencing from the StringConvert function since you pass it by value. All you can do is make the parameter to StringConvert refer to another string, which will have no effect outside the function. In the case where you passed a Class1, you are modifying the reference contained in the object referred to by the parameter, which is the same object referred to in Main. If you had put the line c = new Class1(); as the first line in StringConvert, it would no longer change the value in Main because the parameter in StringConvert would now be referring to a different object.