Re: Deleting exceptions after throwing

From:

James Kanze <james.kanze@gmail.com>

Newsgroups:

comp.lang.c++

Date:

Fri, 25 Sep 2009 00:48:07 -0700 (PDT)

Message-ID:

<6087ac58-5ba3-4409-b213-d794c29532bb@l35g2000vba.googlegroups.com>

On Sep 24, 1:18 pm, p...@informatimago.com (Pascal J. Bourguignon)
wrote:

Emil Berg <emilbe...@gmail.com> writes:

On Sep 24, 1:57 pm, Alan Woodland <aj...@aber.ac.uk> wrote:

Emil Berg wrote:

[snip]

What I want to do is pass exceptions between threads. I
have some exception classes that derive from
CBaseException class. Now I'm doing the following steps:
1. Throw FileNotFoundException on thread A
2. Catch it as CBaseException and save it in an CBaseException*
pointer.
3. Pass this pointer to thread B
4. Throw this exception manually.
5. Catching the exception on thread B as FileNotFoundException
reference

Steps 2,3,4 are part of a threading/messaging
infrastructure that I'm building, so I'd like to delete
the exception on thread B after throwing it (inside the
infrastructure). I don't want the user to delete the
exception.

I hope that I explained it well and maybe you have a good
idea to solve it.

Why not use something like auto_ptr around step 4 so that
when you hit the throw it gets deleted during stack
unwinding?

If I throw auto_ptr<FileNotFoundException> then the user
needs to catch auto_ptr<FileNotFoundException>. I want the
user to catch just FileNotFoundException and not its
auto_ptr.

class TheActualFileNotFoundException:public std::exception {
...};

typedef auto_ptr<TheActualFileNotFoundException> FileNotFoundException;

That doesn't work for inheritance hierarchies. In other words,
if you throw auto_ptr< TheActualFileNotFoundException >, it
won't be caught by:
catch ( auto_ptr< TheActualExceptionBaseType > const& )
Which sort of defeats the purpose of subclassing.

--
James Kanze