I want to create a shared ptr vector of different objects - c++

Question

You have 2 classes Cats and Dogs and need to create a vector of shared pointers which stores the data from those 2 classes. Hints: polymorphism and keep in mind that classes can have similar fields.
So this is what I've done until now. I want to insert in that shared_ptr vector all the info Cats and Dogs classes have, but I don't know how. I only managed to insert in that vector the data from the base class.
#include <iostream>
#include <vector>
#include <memory>
class Animal
{
protected:
int tip;
std::string name;
int age;
public:
Animal(int t, std::string n, int a): tip(t), name(n), age(a) {}
friend std::ostream& operator<<(std::ostream& os, const Animal& a)
{
os << "Name: " << a.name << std::endl;
os << "Age: " << a.age << std::endl;
return os;
}
};
class Cats: public Animal
{
std::string race;
std::string pref_food;
public:
Cats(int t = 0, std::string n = "", int a = 0, std::string r = "", std::string mnprf = ""):
Animal(t, n, a), race(r), pref_food(mnprf) {}
friend std::ostream& operator<<(std::ostream& os, const Cats& c)
{
// auto n = static_cast<Animal> (c);
os << "Name: " << c.name << std::endl;
os << "Age: " << c.age << std::endl;
os << "race: " << c.race << std::endl;
os << "Fav food: " << c.pref_food << std::endl;
return os;
}
};
class Dog: public Animal
{
std::string disease;
std::string master;
public:
Dog(int t = 1, std::string n = "", int a = 0, std::string b = "", std::string s = "" ):
Animal(t, n, a), disease(b), master(s) {}
friend std::ostream& operator<<(std::ostream& os, const Dog& d)
{
os << "Name: " << d.name << std::endl;
os << "Age: " << d.age << std::endl;
os << "disease: " << d.disease << std::endl;
os << "master: " << d.master << std::endl;
return os;
}
};
template<typename T>
void add(std::vector<std::shared_ptr<Animal>>& vec, const T& a)
{
auto newptr = std::make_shared<Animal>(a);
vec.push_back(newptr);
}
int main()
{
std::vector<std::shared_ptr<Animal>> Animals;
Dog d(1,"Rex", 12, "idk", "Oscar");
Cats c(0,"Meaw", 11, "Sfinx", "Catfood");
add(Animals,d);
add(Animals,c);
for(auto i: Animals)
{
std::cout << *i;
}
}

Answer 1

There are a few problems with your code:
Animal lacks any virtual methods. At the very least, it needs a virtual destructor, so that the destructors of Cats and Dog are called correctly when shared_ptr<Animal> calls delete on its held Animal* pointer.
add() is creating an instance of Animal specifically, regardless of T. So your vector contains only real Animal objects. add() needs to create an instance of T instead. A std::shared_ptr<T> can be assigned to a std::shared_ptr<Animal> when T derives from Animal. Of course, add() is redundant, main() can just create and add the new objects directly to its vector without using add() at all.
When main() calls operator<< on an Animal, it will not call the operator<< defined by Cats or Dog, only the operator<< defined by Animal. This can be fixed by having operator<< in Animal call a virtual method that Cats and Dog override. There is no need to define operator<< in derived classes when the base class also has an operator<<.
Try this instead:
#include <iostream>
#include <vector>
#include <memory>
class Animal
{
protected:
int tip;
std::string name;
int age;
public:
Animal(int t, std::string n, int a): tip(t), name(n), age(a) {}
virtual ~Animal() {}
virtual void print(std::ostream& os) const
{
os << "Name: " << name << std::endl;
os << "Age: " << age << std::endl;
}
friend std::ostream& operator<<(std::ostream& os, const Animal& a)
{
a.print(os);
return os;
}
};
class Cat : public Animal
{
std::string race;
std::string pref_food;
public:
Cat(int t = 0, std::string n = "", int a = 0, std::string r = "", std::string mnprf = ""):
Animal(t, n, a), race(r), pref_food(mnprf) {}
void print(std::ostream& os) const override
{
Animal::print(os);
os << "race: " << race << std::endl;
os << "Fav food: " << pref_food << std::endl;
}
};
class Dog : public Animal
{
std::string disease;
std::string master;
public:
Dog(int t = 1, std::string n = "", int a = 0, std::string b = "", std::string s = ""):
Animal(t, n, a), disease(b), master(s) {}
void print(std::ostream& os) const override
{
Animal::print(os);
os << "disease: " << disease << std::endl;
os << "master: " << master << std::endl;
}
};
template<typename T>
void add(std::vector<std::shared_ptr<Animal>> &vec, const T &a)
{
auto newptr = std::make_shared<T>(a);
vec.push_back(newptr);
}
int main()
{
std::vector<std::shared_ptr<Animal>> Animals;
Dog d(1,"Rex", 12, "idk", "Oscar");
Cat c(0,"Meaw", 11, "Sfinx", "Catfood");
add(Animals, d);
add(Animals, c);
/* alternatively:
Animals.push_back(std::make_shared<Dog>(1,"Rex", 12, "idk", "Oscar"));
Animals.push_back(std::make_shared<Cat>(0,"Meaw", 11, "Sfinx", "Catfood"));
*/
for(auto &i: Animals)
{
std::cout << *i;
}
return 0;
}
Output:
Name: Rex
Age: 12
disease: idk
master: Oscar
Name: Meaw
Age: 11
race: Sfinx
Fav food: Catfood
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