[Qt5-feedback] Qt5 and C++ exception

[Дмитрий Б.]

27 июня 2011, 12:25 от Arvid Ephraim Picciani <arvid.picciani at nokia.com>:
> On 06/27/2011 08:26 AM, ext Дмитрий Б. wrote:
> > Sorry guys if this question has already been discussed. Is any plans to
> > make changes in Qt-API to be able to use C++ exceptions, as in the other
> > frameworks?
> > Like this:
> >
> > QThread* thread = new QThread();
> > try
> > {
> > thread->start();
> > }
> > catch (e)
> > {
> > //Error, thread has not been created
> > }
> 
> 
> While this is a simple case (if you ignore abi quirks), consider this:
> 
> class MyWidget: public QWidget {
> private:
> void startStuff();
> {
> thread->start();
> }
> protected:
> virtual void	keyPressEvent ( QKeyEvent * event )
> {
> // if bla
> startStuff();
> }
> }
> 
> 
> 
> What if start() throws now?
> Where do you expect your "catch" ?
> Either way, you can't unwind the eventloop. For once because that could 
> contain native calls that contain no unwind information.
> 
> To get reliable code, you will end up with this:
> 
> void startStuff();
> {
> try {
> thread->start();
> } catch(e) {
> setError(e);
> }
> }
> 

Not really. My understanding that for such situations Qt must have the default exception's handler. 
THis handler for example simply displays a message in QMessageBox. This way it is implemented in VCL-Delphi or in the .NET as i know. Wrap all calls that generate exceptions does not make sense (just defeats the purpose of an exceptions).

This way if you do not want to use default handler:

virtual void	keyPressEvent ( QKeyEvent * event )
{
try {
startStuff1();
startStuff2();
startStuff3();
startStuff4();
startStuff5();
} catch(e)
{
setError(e);
}
}

> 
> Which is exactly what Qt does in the first place, without the boilerplate.
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