Question

i have 2 class: hObject, Drawer. Drawer inherit from hObject.

with this code i retrive a particular object by id:

hObject * foundObj = hManager::getInstance()->getObject("drawer_id");

now i want to correctly cast foundObj from hObject to Drawer. with:

vector<int> points = ((DrawerWidget *)hObject)->getPoints();

i recive

expected primary-expression before ‘)’ token

and what about dynamic cast?

consideration: my skills has been halved till i began c++

Answer 1

Two problems:

• you wrote hObject (the type name) when you meant foundObj (the object name)
• it’s a pointer, so you need to cast to a pointer type (UPDATE: the question has been edited to fix that).

Fixing that, and also using a less dangerous C++-style cast, the following should work:

vector<int> points = (static_cast<DrawerWidget*>(foundObj))->getPoints();

and what about dynamic cast?

If the base class is polymorphic (that is, has at least one virtual function), then that would be safer still – you can check at runtime that the cast is valid:

if (DrawerWidget * dw = dynamic_cast<DrawerWidget*>(foundObj)) {
    vector<int> points = dw->getPoints();
} else {
    // not a DrawerWidget
}

although if you find yourself doing that, I would have a think about the design: it might be more appropriate to redesign the base class to support what you want to do via virtual functions, or to ensure at compile time that the conversion is valid.