CODEWITHSUNDEEP
c++vectoriteratorpolymorphism
Tanatofobico
Tanatofobico

Reputation: 113

vectors containing pointers to polymorphic classes

I have some troubles understanding how to correctly use vectors of pointers in relation with polymorphic classes. Suppose I have a polymorphic structure:

Parent class

class Bumper {

    protected:
    double mu_;

    public:
    Bumper(){};
    Bumper(double mu):mu_(fabs(mu)){};

    void Set_mu(double mu){mu_=mu;};
    virtual void Bounce (Ball & myB)const{myB.change_speed(-sqrt(mu_));};

};

Child class

class ThresholdBumper : public Bumper {

    protected:
    double eps_;

    public:
    ThresholdBumper(double eps):Bumper(1.5), eps_(eps){};

    virtual void Bounce (Ball & myB){
            if(myB.energy()<eps_){Set_mu(1); Bumper::Bounce(myB); Set_mu(1.5); return;};
            Bumper::Bounce(myB);
    };


};

Function

void flipper (Ball & myB, vector<Bumper*> & Obst){
    for(int i=Obst.size()-1; i>=0; i--){
            Obst[i]->Bounce(myB);
    };
};

change_speed() is a void function changing private parameters inside the class Ball, and energy() is a scalar function. This code:

 vector<Bumper*> myBumpers1(10);

 for(int i=0; i<10; i++){
       myBumpers1[i]=new ThresholdBumper(drand48()*5);
 };

 flipper(myBalls2,myBumpers1);

does not work, since Bumper::Bounce() gets called in the "flipper" function. Which means that the function seems to not recognize that there is polymorphism. Can someone explain me why? In particular, redifining the function as:

Function'

 void flipper(Ball & myB, vector<Bumper*>::iterator begin, vector<Bumper*>::iterator end){
    vector<Bumper*>::iterator it;
    for(it=end-1; it!=begin; --it){
            (*it)->Bounce(myB);
    };
};

makes everything work well, as expected. What is the difference exactly?

Upvotes: 0

Views: 58

Answers (1)

user7860670
user7860670

Reputation: 37495

Your child class actually declares separate Bounce function instead of overriding base class Bounce. Notice that in base class it is declared as const. You should redeclare it in child class as

void Bounce (Ball & myB) const override {

override keyword ensures that a virtual function of base class is being overriden

Upvotes: 2

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