hi, i'm experimenting with polymorphism in arduino, but I'm getting the following error message:

bi_grafic.cpp.o: In function ```
gr_routine':
C:\Users\JUANCA~1\AppData\Local\Temp\build4041774866979188726.tmp/bi_grafic.cpp:116: undefined reference to
```

vtable for gr_routine'
C:\Users\JUANCA~1\AppData\Local\Temp\build4041774866979188726.tmp/bi_grafic.cpp:116: undefined reference to `vtable for gr_routine'

does anybody know why :drooling_face:

thanks in advance

bi_grafic.h

```
class gr_routine {
public:
gr_routine();
gr_routine( uint8_t* driver_in );
virtual void execute();
protected:
uint8_t* gr_driver;
};
class routine_a : public gr_routine {
public:
routine_a( uint8_t* driver_in ) ;
virtual void execute();
private:
int a_counter1;
int a_counter2;
int a_counter3;
uint8_t* gr_driver;
};
```

bi_grafic.cpp

```
gr_routine::gr_routine( uint8_t* driver_in ) {
gr_driver = driver_in;
}
gr_routine::gr_routine( ) {
Serial.println("gr_routine_called");
}
routine_a::routine_a( uint8_t* driver_in ) : gr_routine() {
a_counter1 = 1;
a_counter2 = 2;
a_counter3 = 3;
gr_driver = driver_in;
}
void routine_a::execute(){
if (a_counter1 > 7) { a_counter1 = 0; }
if (a_counter2 > 7) { a_counter2 = 0; }
if (a_counter3 > 7) { a_counter3 = 0; }
/* here comes some more code */
a_counter1++;
a_counter2++;
a_counter3++;
}
```