XII virtual function and normal function difference

Virtual function

Mainly to polymorphism. Under normal circumstances, the parent class member functions can not be called a subclass, but once the subclass function is virtual function, then the parent can call the function. Case are as follows:

     Parent *p = new Children();
     //调用 Parent 类中的 method() 方法
     p->method();
     //调用 Children 类中的 virtualMethod() 方法
     p->virtualMethod();

Qt using Virtual Function

Mainly differ in states:

protected:
    /**
     * Q_DECL_OVERRIDE：这个宏表示修饰的函数是对父类虚函数的重载
     */
    void paintEvent(QPaintEvent *event) Q_DECL_OVERRIDE;