Re: Rebirthing an object... just making sure
"Alf P. Steinbach" <alfps@start.no> wrote in comp.lang.c++:
In the first snippet, if ListBox() throws, the listbox object's memory
has been deallocated. In the second snippet, the memory has not been
deallocated. And here there's no easy way to deallocate that memory
if ListBox() throws.
Each dialog box has its own class, something like:
class MonkeyDialog : public Dialog {
public:
ListBox *p_list;
};
The value of p_list is set in the constructor. Presumably like so:
void MonkeyDialog::CreateControls(void)
{
p_list = new ListBox();
}
MonkeyDialog::MonkeyDialog() : p_list(0)
{
CreateControls();
}
MonkeyDialog::~MonkeyDialog()
{
delete p_list;
}
In Snippet B that I originally posted, if the contructor throws, then
"p_list" will contain a non-null address of a has-been-deleted objected.
Therefore, I think I'd have to change Snippet B to:
ListBox *const ptemp = p_list;
delete p_list;
p_list = 0;
::new(ptemp) ListBox();
p_list = ptemp;
....which would probably be better as:
template<class T>
void RebirthObject(T *&pobj)
{
T *const ptemp = pobj;
delete pobj;
pobj = 0;
::new(ptemp) T();
pobj = ptemp;
}
In addition to above comments, clearing a listbox that way could lead
to on-screen flicker, the cost of dynamic allocation in the context of
GUI operations is generally negligible, relatively speaking, and the
only dynamic allocation you avoid is for the listbox object itself,
not for constituents that are referred via pointers or handles.
Use the listbox'es clear function.
The abstract base wxControlWithItems has a method called Clear.
wxRadioBox was intended to inherit from wxControlWithItems, but for some
reason it doesn't. Therefore, the only way to clear the list is to
rebirth.
Don't optimize prematurely.
Admittedly I'm doing it more for kicks than anything else.
--
Tom1s # hilidhe