Dominique LeBlond: see the example

Question

public class MyException : Exception { public MyException ( string message ) : base ( message ) { } } try { if(len>5) throw new MyException(length cannot be > 5); } catch (MyException my) { Console.WriteLine(my.Message); } Output is:length cannot be > 5 I donot know how it come? Can u tell me the sequence of processing of MyException in this example. I want to know where is base constructor

denkai · Answer

The Message property is a public virtual property that only supports get. In essence it is a read-only property and thus the only way to modify it's value is to pass a string message in the constructor. cheers Dom

amit_gupta14 · Answer

U are right that in above case base class constructor will not be called and therefore the base class memebrs will not be initialized. Tell me Is Message property belong to a private member in base class? If No it means Message property is accessible to derive class also. Then it should not matter whether we call base class constructor or not. Am I right?

denkai · Answer

1. In the case you mentioned the base class constructor is no longer called and therefore the base class members are no longer initialized. 2. The diffrence will be that the message property will not be initialized and will use a default: The default is something like this : message = Exception of type  + this.GetType() + was thrown.; 3. Unless you exlicitly call the base class constructor members will not be intialized with your value. Oh and now to really up the ante you can also override the Message property from the Exception class in your MyException class thats called polymorphism. public class MyException : Exception { private string _message; public MyException() { _message = MyException message; } public MyException(string message) { _message = message; } public override string Message { get { return _message; } } } cheers

amit_gupta14 · Answer

Hi Dominique: Can u send me ur mail id I am considering u as my online mentor. You have mentioned above that Console.WriteLine call outputs the value of the base Exception class Message property. . Suppose I call public MyException ( string message ) without base ( message ) sample code: public class MyException : Exception { public MyException(string str) { } } try { if(len>5) throw new MyException(length cannot be > 5); } catch (MyException my) { Console.WriteLine(my.Message); } 1. In this case Myexception is publically derived from Exception. if we call derive class constructor it should call base class constructor also 1st Am I right? 2. If I am right in above case then what's the difference between public MyException(string str) and public MyException(string str):base(str) 3. In above sample code output is coming:Exception of type MyException was thrown. but acc. to me I am passing string length cannot be > 5 to derive class constructor. Message property should be initialized and output shoul be length cannot be > 5

denkai · Answer

The output is correct see other post for details. processing goes a little like this 1. MyException Initialized with string message 2. MyException Initializes base class members with string message. 3. Exception class initializes the Message property with string message. 4. Code throws MyException. 5. MyException caught by catch block. 6. Console.WriteLine call outputs the value of the base Exception class Message property. BTW just reply to the same post if you have additional questions rather than always making a new post. cheers

bilnaad · Answer

?? The output is correct. You derive from Exception //okay You pass the message to the base constructor //okay You throw the Ecxeption //okay You catch the Exception and write the Message to the Console //okay should print length cannot be > 5 This is all correct. But what did you want to achieve?