Exception handling problem

Question

I'm trying to write some code that catches a particular exception and throw a more useful one for something higher up the call stack to deal with but also catch more general exceptions and handle them.

The code is something like this:

try { // Do stuff } catch (SomeException e) { throw new SomeExceptionWithContextInfo(); } catch (Exception e) { // Handle unexpected exception gracefully }

The problem I'm having is that the general exception is catching my new exception. is there a way to avoid this?

My current solution involves checking the type of the exception and throwing it again if it's type is what I just created.

Turns out I wans't catching the correct exceptions so it was working as it should have. — Omar Kooheji
– Omar Kooheji, Commented Mar 17, 2009 at 13:16

Jon Skeet · Accepted Answer · 2009-03-17 11:52:04Z

The code you've posted should work, as shown in this test app:

using System; class OtherException : Exception {} class Test { static void Main(string[] args) { try { Foo(); } catch (OtherException) { Console.WriteLine("Caught OtherException"); } } static void Foo() { try { string x = null; int y = x.Length; } catch (NullReferenceException) { throw new OtherException(); } catch (Exception) { Console.WriteLine("Caught plain Exception"); } } }

This just prints "Caught OtherException" not "Caught plain Exception". Are you sure you don't have a nested try block in your real code? Could you post a short but complete example which shows your problem?

Do you really need to catch Exception in your method though? That's very rarely a good idea.

That's correct, but it there is no try/catch in the Main method, then a plain Exception will be caught, that's what is happening I guess.
If there is no try/catch in the Main method, the application will abort because the exception won't be handled at all.

Tor Haugen · Accepted Answer · 2009-03-17 11:56:21Z

2

You're doing it right. The general exception will not catch the specific one.

answered Mar 17, 2009 at 11:56

Tor Haugen

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Comments

eglasius · Accepted Answer · 2009-03-17 11:59:33Z

The code you posted is the way to do it (catch for more specific exception must appear first).

I suggest looking again at the code, as either they are not in that order, or the code isn't actually throwing that exception type.

Here is a link on msdn about try-catch: http://msdn.microsoft.com/en-us/library/0yd65esw(VS.80).aspx

Björn · Accepted Answer · 2009-03-17 11:52:53Z

Don't catch general exceptions might be the answer? Find out which Exceptions that can be thrown and catch them separately.

try { // Outer try/catch DoSomething(); try { /* */ } catch(NotGeneralException e) { /* */ } catch(AnotherNotGeneralException e) { throw new SomeOtherException("Exception message"); } } catch(SomeOtherException e) { /* */ }

Alternatively only catch a general exception and rethrow SomeOtherExcepion

try { } catch(Exception e) { throw new SomeOtherException("Exception message"); }

I didn't go as far to post a sample app as Jon, but catch work as intended, no need for workarounds - there is surely something else with that code

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