weird error message on dev-cpp

im using dev-cpp as my ide and when i try and compile my project that i'm working on it gives me the following error:

[Linker error] undefined reference to `vtable for ConsItem'

where consItem is a class in this form:

Code:

---

class ConsItem :
      public Item {
public:
ConsItem(Item &acar, Item &acdr) : car(&acar), cdr(&acdr), Item(Cons) {};
virtual ~ConsItem() {};
virtual string toString(); //Turn the Cons item into a string
private:
Item *car;
Item *cdr;
};

---

and the testing code in main like this:

Code:

---

IntegerItem intitem(123);
StringItem stritem("rocks");
cout << stritem.toString() << endl;
cout << intitem.toString() << endl;
   
ConsItem consitem(intitem, stritem);

---

IntegerItem and StringItem and ConsItem all inherit from the same parent class called Item so I assume that i can pass them into ConsItem as Items, maybe i'm wrong? I was wondeirng if anyone else knew what this error means and how to fix it?

You did not define ConsItem::toString();
If you want to make ConsItem pure virtual you have to declare it

Code:

---

virtual string toString()=0; //Turn the Cons item into a string

---

Kurt

yeah i should've defined to string but even with that function gone it still is giving the ( [Linker error] undefined reference to `vtable for ConsItem' ) error. I'm really confused what this error is even saying. Anyone with that has used dev-cpp come across this or know where i can find out about this error message?