problem in downcasting

[yamen ajjour]

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

#include <QtCore/QCoreApplication>
#include <QString>
#include <QLinkedList>
#include <iostream>
using namespace std;
class base
{
    private :
              QString name ;
    public :
              base(QString name )
              {
                this->name=name;
              }
           virtual   void  foo()
              {
 
              }
 
};
 
class child: public base
{
 
    public :
            int num;
            child(QString name , int num):base(name)
            {
                this->num=num;
            }
 
            virtual  void  foo()
            {
 
            }
 
};
int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);
    QLinkedList<base> linkedlist;
    child c("1",1);
    linkedlist.append(c);
       child * p =  dynamic_cast<child *>(&linkedlist.first());
       if(p != NULL)
       {
           // why p is always Null ??
           std::cout<<dynamic_cast<child &>(linkedlist.first()).num;
       }
 
    return a.exec();
}

#include <QtCore/QCoreApplication>
#include <QString>
#include <QLinkedList>
#include <iostream>
using namespace std;
class base
{
    private :
              QString name ;
    public :
              base(QString name )
              {
                this->name=name;
              }
           virtual   void  foo()
              {

              }

};

class child: public base
{

    public :
            int num;
            child(QString name , int num):base(name)
            {
                this->num=num;
            }

            virtual  void  foo()
            {

            }

};
int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);
    QLinkedList<base> linkedlist;
    child c("1",1);
    linkedlist.append(c);
       child * p =  dynamic_cast<child *>(&linkedlist.first());
       if(p != NULL)
       {
           // why p is always Null ??
           std::cout<<dynamic_cast<child &>(linkedlist.first()).num;
       }

    return a.exec();
}

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[nguarracino]

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

You need to have a QLinkedList<base*>. If it's not a list of pointers or references, when you append a child to the list, it will be sliced to a base.