CODEWITHSUNDEEP
c++inheritancemember
kiriloff
kiriloff

Reputation: 26333

Class members and inheritance

I am lost. I have a class Editor and a class Controller. Classes WorkflowEditor and WorkflowController derive from Editor and Controller respectively. Class Controller has a protected member Editor editor and class WorkflowController has a private member WorkflowEditor editor (with same name).

Edit from EitanT:
Here's a simplified code snipped to illustrate what the OP has described:

class Controller
{
    Editor editor;
    // ...
}

class WorkflowEditor : public Editor {
    // ...
};

class WorkflowController : public Controller {
    WorkflowEditor editor;
    // ...
};

My application is a module with graphical interface. In workflow mode, a ribbon appears on Launch, and a wizard is displayed. On click on one button, a method in class Controller is called. Execution crashes because at this time, Editor editor class member of object with type Controller is dead. I would like class member Editor editor to be the same as class member WorkflowEditor editor (same name).

In other words, if a class A has a member of class B and class childA (derived from A) has a member of class childB (derived from B), and member of type childB and B have same name, isn't the member "inherited"?

Upvotes: 0

Views: 123

Answers (2)

Mike Seymour
Mike Seymour

Reputation: 254431

The object is inherited, but is not the same object as the one declared in the derived class. The derived class member is a separate object to the base class member, even though they have the same name. Technically, it hides the base class member, making it accessible only with its qualified name, Controller::editor.

You can achieve what you want with a virtual function, which you override in the derived class to access an object contained there:

class Controller {
public:
    // No data members, just an abstract interface

    // Access a data member of the derived class
    virtual Editor & editor() = 0;
    virtual ~Controller() {}
};

class WorkflowController : public Controller {
public:
    WorkflowEditor & editor() {return editor_;}

private:
    // The object itself - accessible as its true type here, or
    // as its abstract type via the abstract interface.
    WorkflowEditor editor_;
};

Upvotes: 2

Roger Lipscombe
Roger Lipscombe

Reputation: 91825

The member in the derived class hides the member in the base class.

Upvotes: 1

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