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Newsgroups: comp.lang.ada,comp.lang.c++,comp.realtime,comp.software-eng
Subject: Re: Class hierarchy of exceptions (Ada, C++)
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From: Ludovic Brenta <ludovic.brenta@insalien.org>
Date: Mon, 28 Mar 2005 14:21:11 +0200
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Xref: g2news1.google.com comp.lang.ada:10067 comp.lang.c++:47588
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Date: 2005-03-28T14:21:19+02:00
List-Id: <comp.lang.ada>

Ioannis Vranos writes:
> So if you like to be as much constrained as possible, I think VB is
> much better for this. Or even Logo. Plus it provides a turtle to
> help you.

Ah yes, embedded, real-time, certified Logo :)  Come on.

> #include <iostream>
>
>
> class SomeException: public std::exception
> {
>      const char *errorMessage;
>
>      public:
>          SomeException(const char *error):errorMessage(error) {}
>
>          const char *what( ) const throw()
>          {
>              return errorMessage;
>          }
> };
>
>
> int main() try

            ^
Isn't there a missing { here?

> {
>      throw SomeException("Something is wrong!");
> }
>
>
> catch(std::exception &e)
> {
>      std::cerr<<e.what()<<"\n";
> }

And a missing } here?  In which case I don't see any propagation of
your exception up the stack, as there is only one stack frame.

> C:\c>temp
> Something is wrong!
>
> C:\c>
>
>
>
> The exception gets copied as it is propagated up to the stack (with
> the use of the copy constructor). I am not a compiler writer either.

Since you don't provide a copy constructor, only a shallow copy takes
place.  Where is the message string allocated, and how do you know it
is still accessible when you catch the exception in a location remote
from the throw statement?

Also, copying the exception once for each stack frame seems quite
inefficient to me.  I doubt that compiler writers would do that,
especially in the general case of C++ where the exception object can
be arbitrarily large.

-- 
Ludovic Brenta.