我想创建不同对象的共享 ptr 向量

Question

您有 2 个类 Cats 和 Dogs，需要创建一个共享指针向量来存储这 2 个类的数据。提示：多态性并记住类可以有相似的字段。

这就是我到目前为止所做的。我想在 shared_ptr vector 中插入 Cats 和 Dogs 类的所有信息，但我不知道如何。我只设法在vector 中插入来自基类的数据。

#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 缺少任何 virtual 方法。至少，它需要一个virtual 析构函数，以便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。

   李>

2. add() 正在专门创建Animal 的实例，而不管T。所以你的 vector 只包含真正的 Animal 对象。 add() 需要创建 T 的实例。当T 派生自Animal 时，可以将std::shared_ptr<T> 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，而完全不使用add()。

3. 当main()在Animal上调用operator<<时，它不会调用Cats或Dog定义的operator<<，只会调用Animal定义的operator<<。这可以通过让operator<< 在Animal 中调用virtual 方法来解决，该方法Cats 和Dog 覆盖。当基类也有operator<<时，不需要在派生类中定义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

Live Demo