casting error

Hi,
i got a base class,and 2 derieved classes.derieved1 and derieved 2.

In the main class,i create a derieved1 and derieve2 object. add it to vector vector<base*> list .

Then i try casting out the first vector item to see if dereived 1 or derieved2. the tests to check if derieved 1 or 2 work for both.

The classes:

Code:

---

class base{
    protected:
        base(int val){
            value=val;
        }
    public:
        int value;
};

class derieved1:public base {
    private:
        string data;
       
       
    public:
        derieved1(int val,string x):base(val),data(x){ }
        void print(){
            cout<<"\ndereieved 1";
        }
};

class derieved2:public base {
    private:
        string data;
    public:
        derieved2(int val,string x):base(val),data(x){
        }
        void print(){
            cout<<"\ndereieved 2";
        }
};

---

the main function:

Code:

---

int main(int argc, char *argv[])
{
    vector<base*> list;
    derieved1* a=new derieved1(1,"derieved1");
    derieved2* b=new derieved2(2,"derieved2");
   
    list.push_back(a);
    list.push_back(b);
   
    base* bbbb=list[0];
   
    //cast it to both derieved objects.   
    derieved1*sb=static_cast<derieved1*>(bbbb);
   
    derieved2*sb1=static_cast<derieved2*>(bbbb);
   
    //check which one is valid.
   
    if(sb){
          cout<<"object of type derieved1"<<endl;
    }
    if(sb1){
          cout<<"object of type derieved2"<<endl; //should not display
    }
   
    system("PAUSE");
    return EXIT_SUCCESS;
}

---

The program prints outs :

object of type derieved1
object of type derieved2

1. Don't use system(). Very bad habit. Use getchar() or something...
2. If I remember, sb1 points to SOMETHING so it returns true. Also not something you should do everyday. You may check and see if the information it points to is valid. I think....
3. Don't forget to dereference the pointers using the delete operator.

You should be using dynamic_cast, not static_cast.

dynamic_cast will return NULL for a bad pointer cast or throw an exception for a bad reference cast.

i convereted it to:

derieved1*sb=dynamic_cast<derieved1*>(bbbb);
derieved2*sb1=dynamic_cast<derieved2*>(bbbb);


It gives me a error.

'dynamic_cast' : 'base' is not a polymorphic type



what should i modify in the base and derieved classes so that it becomes polymorphic?

The base class should have at least one virtual function. The destructor should be virtual.