C# Cast Exception

Question

Stumbled on some old code that is throwing and empty catching some cast exceptions (about 20 per trip :( )

What if any is the performance hit were taking due to this? Should I be worried about this or is the overhead simply in the try / catch

Surprisingly lacking information on the topic of exception performance with C#.

Thanks, from yours truly.

Answer 1

The exceptions are going to slow you down more than most average lines of code. Instead of casting and then catching the exception, do a check instead. For example

BAD

myType foo = (myType)obj;
foo.ExecuteOperation();

GOOD

myType foo = obj as myType;
if (foo != null)
{
     foo.ExecuteOperation();
}

Answer 2

That's bad for two reasons.

1. Exceptions are slow, there is quite a performance hit. I don't think it'd take an entire millisecond as Matt pointed out, but they are slow enough that you want to avoid them in normal operation.
2. Unless you have a good reason, you shouldn't catch empty exceptions. You're just hiding problems. Better that a program crashes than that it carries on with potentially dangerous bugs.

If they're just try { } finally { } groups, then it's all good -- there's no overhead there. However, try { } catch { } is both potentially dangerous and potentially slow.

As for documentation, this is pretty good: http://www.codeproject.com/KB/architecture/exceptionbestpractices.aspx#Don%27tuseexceptionhandlingasmeansofreturninginformationfromamethod18

Edit: just realized you said empty catching exceptions, not catching empty exceptions. Either way, unless you're dealing with IO, you probably want to avoid doing that for performance's sake.