[mccoyst]

One of his first examples is additionally absurd and is either the flimsiest of strawmen or he simply doesn't understand when exceptions should be used:

    try {
        ...
        int rc = fx ();
        if (rc != 0)
            throw std::exception ("Error!");
        ...
    catch (std::exception &e) {
        handle_exception ();
    }

Why is he throwing exceptions and catching them within the same function? His "C equivalent" is what he should've been doing in C++.

[onli]

He states how he understood exceptions:

"C++ exceptions just didn't fill the bill. They are great for guaranteeing that program doesn't fail — just wrap the main function in try/catch block and you can handle all the errors in a single place."

This is something i learned in my very first computer science lecture not to do.

To be fair: It's what exceptions can be good for - a last barrier before a crash and a way to handle errors later. But you're absolutely right that he simply could react directly to the error. Or throw specific exceptions and react to them. His described issue has nothing to do with exceptions themselves, just with the way he thinks he has to use them.

[figglesonrails]

Exceptions indicate //exceptional conditions//, i.e. conditions other than the intended state transitions of the program. They aren't a guard against crashing, they are a mechanism for formalizing error states in the program.

Memory corruption? Appropriate response: fail. Logic error? Appropriate response: fail. Exception? Appropriate response? Decide if program can continue, respond.

I'd say the bigger issue is less of "exceptions" so much as "states". Adding any kind of error handling increases the number of state conditions that your program may be in, and that complexity is obscenely hard to manage. I don't think C or C++ or Java or Erlang or any other language will free you from the burden of proper software engineering.

[cobrausn]

Though we probably learned this is not the way to use them, I have seen numerous real-world examples where this was the case.

Not only that, I don't think C++ exceptions are necessarily very good at being a 'last barrier' before a crash - they simply can't catch all the errors, because they are good at indicating conditions that might be recoverable, not catching and recovering from logic errors that would cause a crash. There are plenty of ways to hang yourself in C++ without ever throwing an exception.

[figglesonrails]

"Though we probably learned this is not the way to use them, I have seen numerous real-world examples where this was the case."

Ah, Java code at my workplace.

   catch(Exception e) {}

[LoneWolf]

I believe you mean catch(Throwable t) {}

[batista]

>He states how he understood exceptions: "C++ exceptions just didn't fill the bill. They are great for guaranteeing that program doesn't fail — just wrap the main function in try/catch block and you can handle all the errors in a single place." This is something i learned in my very first computer science lecture not to do.

Yes, and he learned not to do it also, thank you.

He makes a tongue in cheek comment about a common Exceptions abuse. Actually, in the very next sentence after than one, he explains why that is bad.

Do people on Hacker News believe that the guy doesn't know C++? He is the frigging author of one of the most useful, used, high quality C++ libs.

[onli]

>Actually, in the very next sentence after than one, he explains why that is bad.

No, he doesn't. The very next sentence is:

"However, what's great for avoiding straightforward failures becomes a nightmare when your goal is to guarantee that no undefined behaviour happens."

[batista]

And that's it, there's nothing more to it.

It's great if your goal is to avoid straightforward failure (= crash), it's bad if your goal is to also avoid undefined behavior (= invalid program state).

Have you discovered something else on the matter?

[onli]

Of course there is. Have you actually read that discussion here? If you don't use exceptions in the way he described them, you don't have undefined behaviour (general big exception handling at the end vs granular error-checking, which is of course also possible with exceptions). Everything he described has nothing to do with exceptions, but with the way he uses them in the examples he showed.

[batista]

>Of course there is. Have you actually read that discussion here?

Yes, and as a Comp Sci, and developer of 15 years, I knew it all before. It's not like the discussion got into any advanced territory.

>If you don't use exceptions in the way he described them, you don't have undefined behaviour (general big exception handling at the end vs granular error-checking, which is of course also possible with exceptions). Everything he described has nothing to do with exceptions, but with the way he uses them in the examples he showed.

Which is the ways that are relevant to his project and coding style. People on the HN thread were just quick to second-guess him without understanding the problem domain and his constraints (which were: "I want to use exceptions in X way for them to be worth to me. I won't even consider the Y way --what some in the HN discussion proposed-- because it's convoluted, requires far more code and maintenance and if I have to do that, I might as well do it in C".

For example, you cannot wrap each and every spot with a try/catch because this doesn't buy you anything over the C way of error checking.

Also, you cannot know what exactly occurred (at coding time, not runtime by checking the stack), unless you granulize (granuralize?) exceptions to death. But then, why not just check the error conditions/codes? And if you do so, what you get over C?

etc...

[rocha]

I agree, it was disconcerting to me as well. I read again and now I think that he is putting the throw there to exemplify that fx() can throw an exception.

[politician]

An ellipsis means something unimportant has been elided. For example,

  try {
      foo();
  catch (std::exception &e) {
      handle_exception ();
  }

  int foo () {
      int rc = fx ();
      if (rc != 0)
      throw std::exception ("Error!");
  }