1.1_nesting_between_classes.cpp

//
// Created by light on 19-12-9.
//

#include <iostream>

class Animal {
public:
    Animal() { std::cout << "Animal() is called" << std::endl; }

    Animal(const Animal &) { std::cout << "Animal (const Animal &) is called" << std::endl; }

    Animal &operator=(const Animal &) {
        std::cout << "Animal & operator=(const Animal &) is called" << std::endl;
        return *this;
    }

    ~Animal() { std::cout << "~Animal() is called" << std::endl; }
};

class Dog {
public:
    // 第一种： 使用初始化列表。
    Dog(const Animal &animal) : __animal(animal) {
        std::cout << "Dog(const Animal &animal) is called" << std::endl;
    }
    // 第二种：构造函数赋值来初始化对象。
    //    Dog(const Animal &animal) {
    //        __animal = animal;
    //        std::cout << "Dog(const Animal &animal) is called" << std::endl;
    //    }
    ~Dog() { std::cout << "~Dog() is called" << std::endl; }

private:
    Animal __animal;
};

int main() {
    Animal animal;
    std::cout << std::endl;
    Dog d(animal);
    std::cout << std::endl;
    return 0;
}