C++ Programming :: Using protected methods within a derived class?


	Using protected methods within a derived class? This doesn't seem to make any sense to me. I have three classes, the declarations of which are shown below: class Action { public: virtual void Act (int range, int elevation, Combatant* actor ) = 0; virtual void React (Action* incoming, Combatant* actor ) = 0; virtual string Name ( ) const = 0; virtual bool CanAct (int range, int elevation, Combatant* actor ) = 0; virtual void Act (int range, int elevation, Combatant* actor, Target& target ) = 0; virtual bool CanAct (int range, int elevation, Combatant* actor, Target& target ) = 0; virtual ~Action() = 0; }; class AttackAction : public Action { protected: virtual void CalculateSpecials (Score* attack, Score* defense ) = 0; virtual void CalculateDamage (Score* attack, Score* defense ) = 0; virtual void DoDamage (int attacker, int defender ) = 0; virtual ~AttackAction() = 0; }; class SpecialAttack : public AttackAction { public: virtual void Act (int range, int elevation, Combatant* actor ); virtual void React (Action* incoming, Combatant* actor ); virtual string Name ( ) const; virtual bool CanAct (int range, int elevation, Combatant* actor ); virtual void Act (int range, int elevation, Combatant* actor, Target& target ); virtual bool CanAct (int range, int elevation, Combatant* actor, Target& target ); virtual ~SpecialAttack(); protected: AttackAction* m_decorated; virtual void CalculateSpecials (Score* attack, Score* defense ); virtual void CalculateDamage (Score* attack, Score* defense ); virtual void DoDamage (int attacker, int defender ); }; Now, inside any of the protected methods of SpecialAttack, if I try this: m_decorated->CalculateSpecials(attack, defense); The compiler spits back the error: error: 'virtual void Battle::AttackAction::CalculateDamage(Battle::Score, Battle::Score)' is protected specialattack.cpp:20: error: within this context Is this something that I've done wrong, or is it a bug within the compiler? It seems intuitively obvious to me that if any of those methods are protected, I should be able to use them within a derived class. Thanks for your help. - Hide quoted text - Tigera wrote: > This doesn't seem to make any sense to me. > I have three classes, the declarations of which are shown below: > class Action > { > public: > virtual void Act (int range, int elevation, Combatant* actor ) = 0; > virtual void React (Action* incoming, Combatant* actor ) = 0; > virtual string Name ( ) const = 0; > virtual bool CanAct (int range, int elevation, Combatant* actor ) = > 0; > virtual void Act (int range, int elevation, Combatant* actor, > Target& target ) = 0; > virtual bool CanAct (int range, int elevation, Combatant* actor, > Target& target ) = 0; > virtual ~Action() = 0; > }; > class AttackAction : public Action > { > protected: > virtual void CalculateSpecials (Score* attack, Score* defense ) = > 0; > virtual void CalculateDamage (Score* attack, Score* defense ) = 0; > virtual void DoDamage (int attacker, int defender ) = 0; > virtual ~AttackAction() = 0; > }; > class SpecialAttack : public AttackAction > { > public: > virtual void Act (int range, int elevation, Combatant* actor ); > virtual void React (Action* incoming, Combatant* actor ); > virtual string Name ( ) const; > virtual bool CanAct (int range, int elevation, Combatant* actor ); > virtual void Act (int range, int elevation, Combatant* actor, > Target& target ); > virtual bool CanAct (int range, int elevation, Combatant* actor, > Target& target ); > virtual ~SpecialAttack(); > protected: > AttackAction* m_decorated; > virtual void CalculateSpecials (Score* attack, Score* defense ); > virtual void CalculateDamage (Score* attack, Score* defense ); > virtual void DoDamage (int attacker, int defender ); > }; > Now, inside any of the protected methods of SpecialAttack, if I try > this: > m_decorated->CalculateSpecials(attack, defense); > The compiler spits back the error: > error: 'virtual void > Battle::AttackAction::CalculateDamage(Battle::Score, Battle::Score)' > is protected > specialattack.cpp:20: error: within this context > Is this something that I've done wrong, or is it a bug within the > compiler? The former. > It seems intuitively obvious to me that if any of those > methods are protected, I should be able to use them within a derived > class. You can, but only on the same object. - Hide quoted text - > Now, inside any of the protected methods of SpecialAttack, if I try > this: > m_decorated->CalculateSpecials(attack, defense); > The compiler spits back the error: > error: 'virtual void > Battle::AttackAction::CalculateDamage(Battle::Score, Battle::Score)' > is protected > specialattack.cpp:20: error: within this context > Is this something that I've done wrong, or is it a bug within the > compiler? It seems intuitively obvious to me that if any of those > methods are protected, I should be able to use them within a derived > class. The protected members of any class can be accessed by friends of the class or pointer/reference to the class derived from it. Although you have derived publicly from class AttackAction but you are invoking it from a pointer to AttackAction. What you are trying to do is akin to this class A { protected: int i; }; A* ptr; ptr->i; //not allowed as i is protected. Try invoking CalculateSpecials directly from within SpecialAttack (which will eventually result in this->CalculateSpecials ) and it should compile fine.