Your answer only works if you know that all your keys are all in the range 1 to 1000000. What if the container has a key of 1000001 in it? Can’t Count that.

This is a great example, bah on the nay-sayers. We are smart enough to know what you mean. Thanks for showing how some simple design decisions and checking can enhance performance!

Keep up the good work, love the blog!

-brian

I guess I could have done a better job explaining the code example. Perhaps a comment here and there would have helped.

My point was not to demonstrate good/realistic algorithm, but to highlight the fact that bad exception handling practice can potentially be harmful to your performance. If it helped, please pretend that the Dictionary is passed to you from somewhere else. I don’t think anybody would write real code like that.

Nice alternate algorithm though.

int notused = 1000000 - numbers.Count;

Yes, using exceptions for non-exception occurences is bad. Dumb algorithms are just as bad.

I agree with your other points. Bad/inappropriate use of exception handling can lead to performance issues and should be avoided.

There is no cost to using try/catch within loops or anywhere else, other than the loss of inlining opportunities.

Costs only arise when exceptions are raised. As a general rule, you should not be relying on exceptions for normal programming tasks. Exceptions are generally for exceptional events, and take up orders of magnitude even outside loops because of stack walking and a variety of other activities.

You had multiple options that avoided the use of exceptions:
1) Use TryGetValue
2) Use ContainsKey