我想创建一个不同对象的共享 ptr 向量

Question

你有 2 个类猫和狗，需要创建一个共享指针向量来存储这 2 个类的数据。提示：多态性，请记住类可以具有类似的字段。

这就是我到目前为止所做的。 我想插入shared_ptrvectorCats和Dogs类的所有信息，但我不知道怎么做。我只设法插入了基类中的数据vector。

#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

您的代码存在一些问题：

1. Animal缺乏任何virtual方法。 至少，它需要一个virtual析构函数，以便在shared_ptr<Animal>在其持有的Animal*指针上调用delete时正确调用Cats和Dog的析构函数。

2. add()正在专门创建Animal的实例，而不考虑T。 因此，您的vector仅包含真实的Animal对象。add()需要改为创建T的实例。 当std::shared_ptr<T>派生自AnimalT时，可以将分配给std::shared_ptr<Animal>。 当然，add()是多余的，main()可以直接创建新对象并将其添加到其vector中，而无需使用add()。

3. 当main()调用operator<<Animal时，它不会调用Cats或Dog定义的operator<<，只会调用Animal定义的operator<<。 可以通过让operator<<Animal调用Cats和Dog重写的virtual方法来解决此问题。 当基类也具有operator<<时，无需在派生类中定义operator<<。

试试这个：

#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;
}

输出：

Name: Rex
Age: 12
disease: idk
master: Oscar
Name: Meaw
Age: 11
race: Sfinx
Fav food: Catfood

现场演示