Throwing an exception.

Question

If I have an error in the program and want to stop the program at that point and throw an exception with my error message, how can I do that? I have been trying to figure this out online, but all I see is throwing an exception with the built in messages.

Thanks,
Arep

A Repasky · Answer

Here is all I had to do. The lead showed me that all I had to do was this. And since I have a try catch in the main program everything goes up to the main. if (( int )dr[ "cnt" ] > 0) { string myEx = "PieceID is zero for JobNumber " + jobID + " on " + dr[ "cnt" ] + " records." ; throw new Exception (myEx); } Thanks, Arep

Vulpes · Answer

That's no problem because an exception will percolate back down the call stack until it's caught or cause the application to fail if it's not caught. So, basically, you need to enclose any call to a library method which can cause a 'fatal' exception (either directly or via a chain of other methods it calls) in a try/catch block within the exe. If that's too tedious, you could also do it globally by handling the AppDomain.UnhandledException event in your exe. This needs to be wired up when your Main() method starts: static void Main(string[] args) { AppDomain currentDomain = AppDomain.CurrentDomain; currentDomain.UnhandledException += MyExceptionHandler; MyClass mc = new MyClass(); mc.MyMethod(); // rest of code } static void MyExceptionHandler(object sender, UnhandledExceptionEventArgs args) { Exception ex = (Exception) args.ExceptionObject; Console.WriteLine(ex.Message); Console.WriteLine("Terminating application ..."); Environment.Exit(1); } Notice that this event will catch any uncaught exception, not just those of type MyException though it's possible to filter the latter out if needed.

A Repasky · Answer

Thanks, I see what has to be done, but my method CheckZero is called from another method in the library. So how does it recognize the throw then? I attached my whole library so you can see it. Plus I have to change some other error message to throw and exception also, so this is not the only one. Everywhere you see me writing out an error message I have to throw an exception. This is something the lead programmer did not tell me about when I started this. Thanks again. Arep

Vulpes · Answer

Well, first of all you need to define your MyException class in the library as public so it will be visible to your exe. You also need to pass your message to the base class's constructor if you want it to be displayed: public class MyException : Exception { public MyException(string str) : base(str) { Console.WriteLine("User Defined Exception"); } } If you then want to engineer a graceful rather than an abrupt termination, you need to catch the exception in your exe and do any necessary cleaning up before terminating the application. So if the code were in a public void method called MyMethod which was within a public class called MyClass in the dll, your code in the exe would be something like this: MyClass mc = new MyClass(); try { mc.MyMethod(); } catch(MyException myEx) { Console.WriteLine(myEx.Message); // clean up code Console.WriteLine("Terminating application ..."); Environment.Exit(1); }

A Repasky · Answer

I forgot to give this code in the last post. class MyException : Exception { public MyException( string str) { Console .WriteLine( "User Defined Exception" ); } }

A Repasky · Answer

That compiles. Here is my code so far. if (( int )dr[ "cnt" ] > 0) { myEx = "PieceID is zero for JobNumber " + jobID + " on " + dr[ "cnt" ] + " records." ; try { throw new MyException (myEx); } catch ( Exception ex) { Console .WriteLine( "Exception " + ex.ToString()); } } I want the program to stop at this point because of the error. This is in a library. I want the error or exception to be passed back to the calling program, then the program will stop and give the console message error. In other words, processing here go back to the main program then give the error. How can I do all this?

Vulpes · Answer

You can use the syntax: throw new Exception(message); 'Exception' can be replaced by a more specific Exception type if you prefer. If this exception is uncaught, then the application will terminate and display the message.

Throwing an exception.

Answers (7)