i've wrote this program and i was trying to make a downcast but it seems the something went wrong !
and by the way can i get rid of foo function ?? it seems that g++ doesn't consider the class base polymorphic if i don't provide a virtual function although i don't need it ! i just want to access the field Num in the way described below
thank you

Qt Code: 
  1. #include <QtCore/QCoreApplication>
  2. #include <QString>
  3. #include <QLinkedList>
  4. #include <iostream>
  5. using namespace std;
  6. class base
  7. {
  8.     private :
  9.               QString name ;
  10.     public :
  11.               base(QString name )
  12.               {
  13.                 this->name=name;
  14.               }
  15.            virtual   void  foo()
  16.               {
  17.  
  18.               }
  19.  
  20. };
  21.  
  22. class child: public base
  23. {
  24.  
  25.     public :
  26.             int num;
  27.             child(QString name , int num):base(name)
  28.             {
  29.                 this->num=num;
  30.             }
  31.  
  32.             virtual  void  foo()
  33.             {
  34.  
  35.             }
  36.  
  37. };
  38. int main(int argc, char *argv[])
  39. {
  40.     QCoreApplication a(argc, argv);
  41.     QLinkedList<base> linkedlist;
  42.     child c("1",1);
  43.     linkedlist.append(c);
  44.        child * p =  dynamic_cast<child *>(&linkedlist.first());
  45.        if(p != NULL)
  46.        {
  47.            // why p is always Null ??
  48.            std::cout<<dynamic_cast<child &>(linkedlist.first()).num;
  49.        }
  50.  
  51.     return a.exec();
  52. }
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