Question

I am trying to get this Zombie/Human agent based simulation running, but I am having problems with these derived classes (Human and Zombie) who have parent class “Creature”. I have 3 virtual functions declared in “Creature” and all three of these are re-declared AND DEFINED in both “Human” and “Zombie”. But for some reason when I have my program call “new” to allocate memory for objects of type Human or Zombie, it complains about the virtual functions being abstract. Here’s the code:

header:

class Creature
{          
public:
      virtual void Attack(Grid G) =0;
      virtual void AttackCreature(Grid G, int attackdirection) =0;
      virtual void Breed(Grid G) =0;
      virtual ~Creature() {}          
      void Die();
      void Move(Grid G);
      int DecideSquare(Grid G);
      void MoveTo(Grid G, int dir);           
};

class Human : public Creature 
{
public:          
      void Attack(Grid G);
      void AttackCreature(Grid G, int attackdirection);
      void Breed(Grid G); //will breed after x steps and next to human          
      int DecideAttack(Grid G);
};

class Zombie : public Creature
{
   public:
      void Attack(Grid G); 
      void AttackCreature(Grid G, int attackdirection);
      void Breed(Grid G) {} //does nothing  
      int DecideAttack(Grid G);
};

cpp:

void Creature::Move(Grid G) {...}
int Creature::DecideSquare(Grid G) {...}
void Creature::MoveTo(Grid G, int dir) {...}
void Creature::Die() {...}
void Human::Breed(Grid G) {...}   
int Human::DecideAttack(Grid G) {...}
void Human::AttackCreature(Grid G, int attackdirection) {...}
int Zombie::DecideAttack(Grid G) {...}
void Zombie::AttackCreature(Grid G, int attackdirection) {...}
void Zombie::Attack(Grid G) {...}

Answer 1

There was a pure virtual function declared: virtual void Creature::Attack(Grid G) but there was no implementation for the derived class Human, i.e. there was no void Human::Attack(Grid G) method defined, which is why I was getting a vtable error. It couldn’t find the source code for the function that I promised. Bad me!