Re: [Boost-users] pimpl and Qt

From: Arne Vogel (Arne.Vogel_at_[hidden])
Date: 2005-05-18 10:38:20

Filipe Sousa wrote:

>Hi!
>
>I'm having trouble implementing Pimpl idiom with Qt. Look at the following 
>code:
>
>class IndispFilterWidget : public QHBox {
>    Q_OBJECT
>public:
>    IndispFilterWidget(QWidget* parent = 0);
>
>private:
>    struct Private;
>    boost::scoped_ptr<Private> d;
>};
>
>struct IndispFilterWidget::Private {
>    QIntDict<BrushButton> buttons;
>};
>
>IndispFilterWidget::IndispFilterWidget(QWidget* parent)
>    : QHBox(parent)
>    , d(new Private)
>{
>}
>
>and see the error:
>
>/usr/include/boost/checked_delete.hpp: In function 'void 
>boost::checked_delete(T*) [with T = 
>exames::calendario::IndispFilterWidget::Private]':
>/usr/include/boost/scoped_ptr.hpp:77:   instantiated from 
>'boost::scoped_ptr<T>::~scoped_ptr() [with T = 
>exames::calendario::IndispFilterWidget::Private]'
>/home/fsousa/projects/GAL/BUILD/modules/exames/calendario/../../../../modules/exames/calendario/IndispFilterWidget.h:31:   
>instantiated from here
>/usr/include/boost/checked_delete.hpp:32: error: invalid application of 
>'sizeof' to incomplete type 'exames::calendario::IndispFilterWidget::Private' 
>/usr/include/boost/checked_delete.hpp:32: error: creating array with size zero 
>('-0x000000001')
>/usr/include/boost/checked_delete.hpp:33: error: invalid application of 
>'sizeof' to incomplete type 'exames::calendario::IndispFilterWidget::Private' 
>/usr/include/boost/checked_delete.hpp:33: error: creating array with size zero 
>('-0x000000001')
>/usr/include/boost/checked_delete.hpp:34: warning: possible problem detected 
>in invocation of delete operator:
>/usr/include/boost/checked_delete.hpp:29: warning: 'x' has incomplete type
>/home/fsousa/projects/GAL/BUILD/modules/exames/calendario/../../../../modules/exames/calendario/IndispFilterWidget.h:45: 
>warning: forward declaration of 'struct 
>exames::calendario::IndispFilterWidget::Private'
>
>If I remove Q_OBJECT macro or add a destructor the code compiles fine. I don't 
>have a problem with shared_ptr, only with scoped_ptr.
>  
>
scoped_ptr cannot be used with incomplete types, unfortunately, and thus 
is not available for use in the pimpl idiom.
You can:

1. Use shared_ptr.
2. Use a regular pointer and delete it in the class destructor (in the 
implementation file).
3. Not much else you can do. Write your own incomplete_scoped_ptr, 
maybe. :o)