What are the dangers of try...catch when Catch loop is empty?

Question

Hi All I have been bomb proofing a bit code today I have found the try catch statement does it nicely I did have the catch loop as below to tell me something had blown up and I could then track down what had pooped and sort it as below: catch { MessageBox.Show(ERROR); } but investigation led nowhere so I commented out the MessageBox and problem solved or masked over? I will run it on a different PC to see if this has cured the fault if it has how? Glenn

Vulpes · Answer

You can get more information about the error with: catch(Exception ex) { MessageBox.Show(ex.Message); } Sometimes an exception is non-fatal and you can simply 'swallow' it and carry on. However it's unwise to do this without knowing what caused the exception in the first place. It may come back and bite you (or worse still your client) later. A good strategy is to check the MSDN docs to see what exceptions can be thrown by the various .NET Framework methods and properties and try to catch those exceptions specifically.

Glenn Patton · Answer

I have just tested it again in circumstances that were certain to result in the Exception. Still nothing ah well out the door it goes! Thanks for the help.

Vulpes · Answer

Perhaps you've inadvertently changed something which has fixed the problem ? But in my experience clients don't mind the odd error if it's handled gracefully. What they don't like is when the app blows up with no opportunity for remedial action.

Glenn Patton · Answer

I have been trying to get it to go wrong all day it stubbornly works. Frustrating

Vulpes · Answer

Well it might help you to figure it out if you knew what intermittent exception was being thrown. Can you keep on trying whatever it is you're doing until eventually an exception is thrown?

Glenn Patton · Answer

Why are they not re-occurring that is what's bothering me the thing is this might have to go out door to a client. Who will then possibly (probably) raise issue causing lots of aggro....

Vulpes · Answer

I don't know but if you're having them you'll have to leave the try/catch in otherwise they'll bring your application down when they occur. Sometimes you can implement a 'retry' strategy when an intermittent fault occurs particularly if it's hardware related and the user may be able to do something about it before trying again. The basic code for 'retry' is: retry: try { // code } catch (Exception ex) { string temp = ex.Message + 

 + Do you want to try again?); DialogResult dr = MessageBox.Show(temp Error MessageBoxButtons.YesNo); if (dr == DialogResult.Yes) goto retry; }

Glenn Patton · Answer

That makes sense as I have commented out the try...catch and it works no issue. What I would like to know is why ******* intermittent faults!

Vulpes · Answer

Code within catch blocks only executes if there's an exception of the governing type for that catch block. So if there's no exception in the try block  the code in the catch clause(s) will not execute and execution will pass to the following statement in the normal way. Consequently as we've written the code in such a way that it will catch ALL exceptions and print some message then if no message pops up there's no exception being thrown.

Glenn Patton · Answer

So that what I thought no message means no exception. Why???

Vulpes · Answer

The warning is telling you what we already knew (or thought we knew) that all exceptions are derived from System.Exception and therefore the 'empty' catch is unnecessary. So if the MessageBox is still not popping up then no exception is being thrown.

Glenn Patton · Answer

Modified code still problem solved. Has problem been solved or not happened? Testing testing 1 2 3 Testing mind you the below warning cropped up: Warning 1 A previous catch clause already catches all exceptions. All non-exceptions thrown will be wrapped in a System.Runtime.CompilerServices.RuntimeWrappedException. G:\PitStopTest\CommsTester using Delegates Error Checking\C#CommsTesterEventHandler\Form1.cs 1784 13 RS232CommPort I'm always nervous of warnings! Glenn

Vulpes · Answer

It should always display something as all exceptions in .NET ultimately derive from System.Exception. Perhaps there's no exception being thrown? To make absolutely sure there's nothing funny going on try this 'belt and braces' approach: try { // code} } catch(Exception ex) { if (!String.IsNullOrEmpty(ex.Message)) { MessageBox.Show(ex.Message); } else { MessageBox.Show(an exception occurred with no message); } } catch { MessageBox.Show(A 'funny' exception occurred); }

Glenn Patton · Answer

The try...catch(ex.Message) MessageBox.Show(ex.Message); Is not displaying anything have I swallowed it? Glenn

Glenn Patton · Answer

In other words fiddle more! Thanks Glenn