Re: Deleting exceptions after throwing

From:

Emil Berg <emilbergg@gmail.com>

Newsgroups:

comp.lang.c++

Date:

Sat, 26 Sep 2009 23:06:15 -0700 (PDT)

Message-ID:

<63f6f41e-c43d-4064-9486-e2e518799456@k26g2000vbp.googlegroups.com>

On Sep 25, 10:48 am, James Kanze <james.ka...@gmail.com> wrote:

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

* When I override Clone() in each child class, I write the following
line of code (For instance, in the class of FileNotFound):
return auto_ptr<CloneableException>(new FileNotFoundException(*this));
* When I override Throw() in each child clss, I write the following:
throw *this;

*When catching in the middle I use the following:
catch (const CloneableException& ex)
{
exPassed = ex.Clone();
}

*Then I rethrow it this way:
CloneableException* ex = exPassed.get();
ex->Throw();

*At the end I catch it this way:
catch(const FileNotFoundException& ex)

And it worked for me.
Thanks!