[Interest] type casting 5 levels down no error but not proper

[BERAUD Alexandre]

The reason is that the scrollarea is NOT the parent of the sheet. You 
must check every single pointer that you get from a cast. If you use a 
debugger you can dig a bit and discover whether your sheet's parent is 
null or some other class, but it is certainly not a QScrollArea. Anyway, 
don't use cascading casts like this, there are a lot of other methods, 
even ugly ones, but not as ugly (and dangerous) as this. Store your 
mainwin in a global variable, or pass it as an argument to the class 
contructor.

Regards.

Alex


Le 24/04/2012 15:27, Sujan Dasmahapatra a écrit :
> [code]
> QWidget *wid  = qobject_cast<QWidget *>(parent());
> CSheet *sheet = qobject _cast<CSheet *>(wid->parent());
> QScrollArea *scrollArea = qobject _cast<QScrollArea *>(sheet->parent());
> CTabWidget *tabWid = qobject _cast<CTabWidget *>(scrollArea->parent());//Here it is crashing, QSSERT(d)  failure
> CDataPage  *dataPage = qobject _cast<CDataPage *>(tabWid->parent());
> MainWindow *mainwin = qobject _cast<MainWindow *>(dataPage->parent());
> mainwin->statusBar()->showMessage(tr("A new plot being added!!"),5000);
> [/code]
>
> Dear Konstantin
>
> It's not returning anything, it's crashing. When casting to get CTabWidget. For the sheet's parent is QScrollBar so I am getting that by scrollArea and scrollArea's parent is CTabWidget.....which is getting failure. What could be the possible reason, please help.
>
> Kind regards,
>
>
> Sujan Dasmahapatra
> Project Leader, Aero Group
> CE - Aero Group
>
> Tel  +91 80 66470248
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> sdh at lmwindpower.com
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> -----Original Message-----
> From: Konstantin Tokarev [mailto:annulen at yandex.ru]
> Sent: Tuesday, April 24, 2012 6:17 PM
> To: Sujan Dasmahapatra
> Cc: interest at qt-project.org
> Subject: Re: [Interest] type casting 5 levels down no error but not proper
>
>
> 24.04.2012, 16:42, "Sujan Dasmahapatra"<sdh at lmwindpower.com>:
>> Thanks Diego and Konstantin for your valuable inputs. I am now doing qobject_cast for all of them, please check the code snippet below, now it’s crashing at tabWid step. It’s giving QASSERT failure. The failure is happening in the following file
>>
>> //qscopedpointer.h at the following line QASSERT(d)
>>
>>    inline T *operator->() const
>>
>>      {
>>
>>          Q_ASSERT(d); //this line it’s crashing.
>>
>>          return d;
>>
>>      }
> It means that tabWid is QScopedPointer with 0 value. You need to check if qobject_cast doesn't return 0 before using pointer.
>


-- 
Alexandre BERAUD
Ingénieur Développement
INFFLUX
01.49.57.92.00