How can I check price of each sub class? - c++

Question

class Attraction {
};
class Museum : public Attraction {
private:
double price;
public:
void setPrice(double Price) {
price = Price;
}
double getPrice() {
return price;
}
};
class Park : public Attraction {
public:
double getPrice() {
return 0;
}
};
class Theatre : public Attraction {
private:
double price;
public:
void setPrice(double Price) {
price = Price;
}
double getPrice() {
return price;
}
};
int _tmain(int argc, _TCHAR* argv[]) {
vector<Attraction> attraction;
vector<Attraction>::iterator i;
for (i = attraction.begin(); i != attraction.end(); i++) {
if (i->getPrice() < 5) {
cout << endl;
}
}
}

Answer 1

vector<Attraction> performs object slicing, so you can never access getPrice() of derived classes. You need to use polymorphism instead, where you have a virtual double GetPrice() method in the Attraction class, and then use vector<Attraction*> with new/delete for the objects. Don't forget to make the destructor in Attraction virtual as well, so you can delete descendant object using a base pointer.

Answer 2

What you are attempting to do is not possible with the code you have shown. You are not utilizing polymorphism correctly.
Try something more like this instead:
class Attraction
{
public:
Attraction() {}
virtual ~Attraction() {}
virtual double getPrice(double Price)
{
return 0.0;
}
};
class PriceyAttraction : public Attraction
{
private:
double price;
public
PriceyAttraction(double Price = 0.0) : Attraction(), price(Price) {}
virtual double getPrice()
{
return price;
}
void setPrice(double Price)
{
price = Price;
}
};
class Museum : public PriceyAttraction
{
public:
Museum(double Price = 0.0) : PriceyAttraction(Price) {}
};
class Park : public Attraction
{
public:
Park() : Attraction() {}
};
class Theatre : public PriceyAttraction
{
public:
Theatre(double Price = 0.0) : PriceyAttraction(Price) {}
};
int _tmain(int argc, _TCHAR* argv[])
{
std::vector<Attraction*> attraction;
attraction.push_back(new Museum(5.00));
attraction.push_back(new Park);
attraction.push_back(new Theatre(7.50));
std::vector<Attraction*>::iterator i;
for (i = attraction.begin(); i != attraction.end(); ++i)
{
std::cout << i->getPrice() << std::endl;
//...
}
for (i = attraction.begin(); i != attraction.end(); ++i)
{
delete *i;
}
}
If you are using C++11 or later, you can use std::unique_ptr to manage the object deallocations for you:
int _tmain(int argc, _TCHAR* argv[])
{
std::vector<std::unique_ptr<Attraction>> attraction;
attraction.emplace_back(new Museum(5.00));
attraction.emplace_back(new Park);
attraction.emplace_back(new Theatre(7.50));
/* or:
attraction.push_back(std::unique_ptr<Attraction>(new Museum(5.00)));
attraction.push_back(std::unique_ptr<Attraction>(new Park));
attraction.push_back(std::unique_ptr<Attraction>(new Theatre(7.50)));
*/
/* or:
attraction.push_back(std::make_unique<Museum>(5.00));
attraction.push_back(std::make_unique<Park>());
attraction.push_back(std::make_unique<Theatre>(7.50));
*/
vector<Attraction>::iterator i;
for (i = attraction.begin(); i != attraction.end(); ++i)
{
std::cout << (*i)->getPrice() << std::endl;
//...
}
}