Copy all parts of an object.

在实现Derived类的copy constructor和copy assignment的时候，不仅要copy derived类的成员，还要拷贝base类的成员。


#include <string>
#include <iostream>class Animal
{public:Animal(const std::string & name, int age) : m_name(name),m_age(age){std::cout << "Animal ctor called." << std::endl;}
protected:std::string m_name;int m_age;
public:Animal(const Animal &animal) {m_name = animal.m_name;m_age = animal.m_age;}Animal & operator=(const Animal &animal) {m_name = animal.m_name;m_age = animal.m_age;return *this;}
};class Dog : private Animal
{public:Dog(const std::string &name, int age, const std::string &color) : Animal(name, age), m_color(color) {std::cout << "Dog ctor called." << std::endl;}Dog(const Dog &dog) : Animal(dog.m_name, dog.m_age) {m_color = dog.m_color;}Dog &operator=(const Dog &dog) {Animal::operator=(dog);m_color = dog.m_color;return *this;}
protected:std::string m_color;
};int main() {Animal aanimal("dog", 9);Dog adog("huabao", 5, "red");Dog bdog("xinba", 6, "yellow");adog = bdog;  Dog cdog(adog);return 0;
}

由于拷贝对象是每一个成分都需要拷贝，即derived类实现copy ctor和copy assignment时需要调用base类的copy ctor和copy assignment，因此如果想禁用(derived)类的copy函数，只需要将base类的copy函数禁用即可，可将base类的copy ctor和copy assignment设置成private（只需声明，不需要实现）即可。也可使用delete实现。

#include <string>
#include <iostream>class Animal
{public:Animal(const std::string & name, int age) : m_name(name),m_age(age){std::cout << "Animal ctor called." << std::endl;}
protected:std::string m_name;int m_age;
private:Animal(const Animal &animal);Animal & operator=(const Animal &animal);
};class Dog : private Animal
{public:Dog(const std::string &name, int age, const std::string &color) : Animal(name, age), m_color(color) {std::cout << "Dog ctor called." << std::endl;}
#if 0  // 由于base类禁用了copy函数,因此这里无法实现Dog(const Dog &dog) : Animal(dog) {m_color = dog.m_color;}Dog &operator=(const Dog &dog) {Animal::operator=(dog);m_color = dog.m_color;return *this;}
#endif
protected:std::string m_color;
};int main() {Animal aanimal("dog", 9);Dog adog("huabao", 5, "red");Dog bdog("xinba", 6, "yellow");
#if 0  // 非法调用adog = bdog;  Dog cdog(adog);
#endifreturn 0;
}

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