C++ - 打印派生类对象的矢量<base*> 元素

我有一个名为Pet的抽象类和三个派生类CatDogGoldfish。我正在尝试将它们存储在矢量中，并打印宠物的名字。但是我得到了一些十六进制数字。我不知道我哪里做错了。

// Here is pet.h
#ifndef PET_H
#define PET_H
#include<iostream>
using namespace std;
class Pet
{
public:
//constructor
Pet(string);
// virtual destructor
virtual ~Pet();
// pure virtual function
virtual string speak() = 0;
//getters setters
string getName();
//overloading comparative operators
bool operator< (Pet&);
friend ostream& operator<<(ostream&, Pet&);
protected:
string pet_name; //name of pet
};

#endif // PET_H

Here is pet.cpp
#include <iostream>
#include "Pet.hpp"
#include <string>
using namespace std;
//constructor
Pet::Pet(string name) : pet_name(name)
{}
//overloading comparator function
bool Pet::operator<(Pet& obj)
{
return ((pet_name.compare(obj.pet_name)) < 0);
}
//getter for name
string Pet::getName() { return pet_name; }
// destructor
Pet::~Pet() { /* dtor */ }

ostream& operator<<(ostream& output, Pet& p) {
output << "I am pet";
return output;
}

#ifndef CAT_H
#define CAT_H
#include "Pet.hpp"
class Cat: public Pet
{
public:
Cat(string);
virtual ~Cat();
string speak();
friend ostream& operator<<(ostream &, Cat&);
};
#endif // CAT_H

#include "Cat.hpp"
#include<string>
Cat::Cat(string name):Pet(name)
{
//ctor
}
string Cat::speak()
{
return ">>Meow Meow>>";
}
Cat::~Cat()
{
//dtor
}

ostream& operator<<(ostream& output, Cat& p) {
output << "I am " << p.getName() << " " << p.speak() << endl;
return output;
}

List.hpp文件

#ifndef LIST_H
#define LIST_H
#include<iostream>
#include <vector>
#include<algorithm>
using namespace std;
template<class T>
class List
{
public:
void add_item(T);
void sortList();
void print();
private:
vector<T> list;
};

template<class T>
void List<T>::add_item(T item_list) {
list.push_back(item_list);
}
template<class T>
void List<T>::sortList() {
sort(list.begin(), list.end());
}

template<class T>
void List<T>::print() {
std::vector<T>::iterator i;
for (i = list.begin(); i != list.end(); ++i) {
cout << *i << endl;
}
}

#endif // LIST_H

这是的主要功能

int main()
{
List<Pet*> pets;
// book items adding in the lists
pets.add_item(new Cat("Kitty"));
pets.add_item(new Cat("Tom"));

// sorting lists
pets.sortList();
// printing lists
// ----- Here is the PROBLEM ------
pets.print(); // --> Here I am getting problem
// --> when this statement executes, I get the hexa decimal number

// saving in files
return 0;
}