Why throw a new exception rather than the one caught?

[andegre]

http://msdn.microsoft.com/en-us/library/xhcbs8fz(v=VS.80).aspx

This article talks about throwing exceptions, but my question is why do they say to throw a new exception, of the same type, but with a different title(?)?

Why not just say:

catch (Exception ex)
{
   throw;
}

as opposed to:

catch (Exception ex)
{
    throw new Exception("my repetitive exception", ex);
}

Just curious...

 

[jmeckley]

you can use the new error to create a friendly error message for the end user and log the actual error some place else. I would take it one step farther though, and create a another subtype from Exception.

class FriendlyUserException : Exception
{
   public FriendlyUserException(string message, Exception actual)
   : base(message, actual)
}

try
{
   ...
}
catch(Exception e)
{
   throw new FriendlyUserException("Ouch, something went wrong.", e);
}

Jason Meckley
Programmer

faq855-7190
faq732-7259

 

[oharab]

To expand on jmeckly's answer, I often use custom exceptions that contain more details about the context the exception occurred in, so storing things like repository names/connection strings, current user, etc so that when they are caught, there's more infomation available to help you.


----------------------------------------------
Ben O'Hara

http://www.RobotParade.co.uk

We could be confused in exactly the same way, but confusion might be like Nulls, and not comparable.

 

[andegre]

oharab, do you just output that information in a big string, or a datatable? That's a great idea but I'm trying to figure out how to make it work with our exception handling system.

We just write all of our exceptions to a table, and only save the message, stack trace, additional info, machine name, user....that's about it. I guess I could expand the message field and have that contain much more info after the regular message.

 

[oharab]

Depends what I'm doing & what logging is in place.
Generally I use log4net so I can change my logging needs on the fly.
Some systems log errors into a database, some just write everything to a text file, others email me when fatal errors occur. Using log4net lets me set these options as needed, so I only turn debug logging on when there's an issue I'm trying to fix, etc.




----------------------------------------------
Ben O'Hara

http://www.RobotParade.co.uk

We could be confused in exactly the same way, but confusion might be like Nulls, and not comparable.