Re: Rebirthing an object... just making sure
On Jan 9, 10:47 am, "Tom=E1s =D3 h=C9ilidhe" <t...@lavabit.com> wrote:
"Alf P. Steinbach" <al...@start.no> wrote in comp.lang.c++:
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;
You doubtlessly mean "p_list->~ListBox" here.
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;
Again: "pobj->~T()"
pobj = 0;
::new(ptemp) T();
pobj = ptemp;
}
And of course, if the constructor of T throws, you still leak
the memory. You really need something like:
template< typename T >
void
renewObject( T*& obj )
{
// Fail if object has a derived type...
assert( typeid( *obj ) == typeid( T ) ) ;
obj->~T() ;
try {
new( obj ) T ;
} catch ( ... ) {
::operator delete( obj ) ;
obj = NULL ;
throw ;
}
}
--
James Kanze (GABI Software) email:james.kanze@gmail.com
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