Re: Help Me Please :)

[Robert A Duff <bobduff@world.std.com>]

"James S. Rogers" <jimmaureenrogers@worldnet.att.net> writes:

> Have you ever used exceptions in C++? 

No.  The last time I used C++ (some years ago), most compilers did not
support exceptions.  The closest I could get was reading about them in
Stroustrup's book.  But I have used exceptions in other languages that
define exceptions as first-class objects.

>...Very few people do.
> The problem arises from the fact that exceptions are first class objects.

I don't understand this problem.  Perhaps you could give an example?  Is
the problem you're talking about C++-specific, or are you claiming it's
a fundamental problem with the idea of exceptions-as-objects?

One problem I see with C++ exceptions is that anything can be an
exception -- you can throw a string or an int or whatever.  I would
prefer to have a distinguished exception class, and then you could
define new exceptions by subclassing that.  Several other languages that
have first-class exceptions do exactly that.  But this seems like a
minor issue.

> In C++ you cannot "catch" an exception without knowing its type. This means
> that you must have exquisite coupling with all your dependent compilation
> units
> to use exceptions reliably. This coupling requirement works strongly against
> encapsulation and modularity.

Again, I don't get it.  Of course you can't catch an exception without
knowing its type.  Just like in Ada you can't handle an exception
without knowing its name.  I don't see how that breaks encapsulation and
modularity.

> The only way around this is to declare a single exception type for all
> exceptions
> generated by an application. This leaves you in the same position as you are
> in Ada.  Of course, the problem with this solution for C++ is that you will
> probably use
> class libraries, which, if they use exceptions at all, will probably not
> conform to the
> exception class chosen by your team. If this is the case, then you are in a
> much
> worse situation than if you used Ada.

- Bob