Re: any_function (callback) library

From: williamkempf_at_[hidden]
Date: 2001-04-12 08:42:47

--- In boost_at_y..., "David Abrahams" <abrahams_at_m...> wrote:
> 
> ----- Original Message -----
> From: <williamkempf_at_h...>
> To: <boost_at_y...>
> Sent: Wednesday, April 11, 2001 6:43 PM
> Subject: [boost] Re: any_function (callback) library
> 
> 
> > --- In boost_at_y..., "David Abrahams" <abrahams_at_m...> wrote:
> > >
> > > ----- Original Message -----
> > > From: <williamkempf_at_h...>
> > >
> > > > C++ platforms (MSVC) that throw exceptions when an assertion
> > fires?
> > > > Some alternative library assertion packages may do this, but 
none
> > > > that come with MSVC throw exceptions.  I was speaking of other
> > > > languages here.
> > >
> > > What does this program do with msvc?
> > >
> > > include <cassert>
> > > #include <iostream>
> > >
> > > int main() {
> > >     try {
> > >         assert(0);
> > >     }
> > >     catch(...) {
> > >         std::cout << "hi there" << std::endl;
> > >     }
> > >     return 0;
> > > }
> > >
> > > Try compiling it as follows:
> > >     cl /MLd /GX /EHa foo.cpp
> >
> > It halts the program.  Even if you Ignore the assertion the catch
> > block is never entered.  Like I said, none of the assertion 
libraries
> > that come with MSVC throw exceptions.
> 
> That's incorrect. You obviously didn't try it.

Whoa.  Slow down there.  This comes very close to flame material, 
especially considering I *DID* check it (VC 6, SP 4), and I'm correct 
that the catch block is never entered.  Sorry.

> It throws a structured
> exception which raises JIT debugging. First you get an abort/retry 
dialog.
> Then you choose "Retry" to enter JIT debugging. Then it prints "hi 
there" to
> standard out as the structured exception enters the catch block. 
Then the
> JIT debugger fails to come up because the exception isn't re-thrown.

Not on my tests it doesn't.  However, I ran this test under the 
debugger.  Possibly the behavior you speak of only occurs when run 
outside of the debugger.  That would be an interesting case, but one 
that I've never encountered since I only run debug builds through the 
debugger.
 
> > Again, std::vector::at() exists for precisely this reason, and C++
> > programmers use it in precisely the same manner as IndexError is
> > used.  I don't agree that we have a completely different culture 
in
> > this case.  There are many C++ programmers that want, even need, 
to
> > insure their programs never crash... that they can catch errors,
> > possibly handle them, and continue running.
> 
> ...mmm, I don't think I agree. Would anybody really do this in C++?
> 
> for (std::size_t i = 0;; ++i)
> {
>     T* x;
>     try {
>         x = &v.at(i);
>     }
>     catch(std::out_of_range) {
>         break;
>     }
>     f(*x);
> }

Yes, people really do that, though this particular case is so simple 
that a rewrite can easily be done to insure out of range checks are 
not needed.  So I'd expect qualified C++ programmers would avoid 
this.  Then again, I'd expect qualified language X programmers to 
avoid it as well (and have seen them do so).

Bill Kempf