首页 > 代码库 > c++第十章-（多继承与虚继承）
c++第十章-（多继承与虚继承）
多继承
class Person{public: Person(std::string theName); void introduce(); protected: std::string name;};class Teacher : public Person{public: Teacher(std::string theName,std::string theClass); void teach(); void introduce(); protected: std::string classes;};class Student : public Person{public: Student(std::string theName,std::string theClass); void attendClass(); void introduce();protected: std::string classes;};Person::Person(std::string theName){ this->name = theName;}void Person::introduce(){ std::cout << "大家好，我是" << name << ".\n\n";}Teacher::Teacher(std::string theName,std::string theClass) : Person(theName){ this->classes = theClass;}void Teacher::teach(){ std::cout << this->name << "教" << classes << ".\n\n";}void Teacher::introduce(){ std::cout << "大家好，我是" << name << "，我教" << classes << ".\n\n";}Student::Student(std::string theName,std::string theClass) : Person(theName){ this->classes = theClass;}void Student::attendClass(){ std::cout << name << "加入" << classes << "学习。\n\n";}void Student::introduce(){ std::cout << "大家好，我是" << name << "，我在" << classes << "学习.\n\n";}class TeachingStudent : public Student,public Teacher{public: TeachingStudent(std::string theName,std::string classTeaching,std::string classAttending); void introduce();};TeachingStudent::TeachingStudent(std::string theName,std::string classTeaching,std::string classAttending) : Teacher(theName,classTeaching),Student(theName,classAttending){ }void TeachingStudent::introduce(){ std::cout << "大家好，我是" << Student::name << ".我教" << Teacher::classes << ","; std::cout << "同时我在" << Student::classes << "学习.\n\n";}int main(int argc, const char * argv[]){ Teacher teacher("小甲鱼","C++入门班"); Student student("迷途羔羊","C++入门班"); TeachingStudent teachingStudent("丁丁","C++入门班","C++进阶版"); teacher.introduce(); teacher.teach(); student.introduce(); student.attendClass(); teachingStudent.introduce(); teachingStudent.teach(); teachingStudent.attendClass(); return 0;}
控制台返回结果是：
大家好，我是小甲鱼，我教C++入门班.小甲鱼教C++入门班.大家好，我是迷途羔羊，我在C++入门班学习.迷途羔羊加入C++入门班学习。大家好，我是丁丁.我教C++入门班,同时我在C++进阶版学习.丁丁教C++入门班.丁丁加入C++进阶版学习。
虚继承
TeachingStudent对象里继承了2个不同的classes属性，也就说也继承了2个不同的name属性。
但当我们的预期是同一个人的时候去做2件不同事的时候，就存在分裂多1个不必要的人了！就TeachingStudent类继承于Teacher和Student两个类，因而继承了两组Person类的属性。这个时候Person类的name属性就会引起麻烦。
class Person{public: Person(std::string theName); void introduce(); protected: std::string name;};class Teacher : public Person{public: Teacher(std::string theName,std::string theClass); void teach(); void introduce(); protected: std::string classes;};class Student : public Person{public: Student(std::string theName,std::string theClass); void attendClass(); void introduce();protected: std::string classes;};Person::Person(std::string theName){ this->name = theName;}void Person::introduce(){ std::cout << "大家好，我是" << name << ".\n\n";}Teacher::Teacher(std::string theName,std::string theClass) : Person(theName){ this->classes = theClass;}void Teacher::teach(){ std::cout << this->name << "教" << classes << ".\n\n";}void Teacher::introduce(){ std::cout << "大家好，我是" << name << "，我教" << classes << ".\n\n";}Student::Student(std::string theName,std::string theClass) : Person(theName){ this->classes = theClass;}void Student::attendClass(){ std::cout << name << "加入" << classes << "学习。\n\n";}void Student::introduce(){ std::cout << "大家好，我是" << name << "，我在" << classes << "学习.\n\n";}class TeachingStudent : public Student,public Teacher{public: TeachingStudent(std::string theName1,std::string theName2,std::string classTeaching,std::string classAttending);// void introduce();};TeachingStudent::TeachingStudent(std::string theName1,std::string theName2,std::string classTeaching,std::string classAttending) : Teacher(theName1,classTeaching),Student(theName2,classAttending)//{ }void TeachingStudent::introduce(){ std::cout << "大家好，我是" << Student::name << ".我教" << Teacher::classes << ","; std::cout << "同时我在" << Student::classes << "学习.\n\n";}int main(int argc, const char * argv[]){ Teacher teacher("小甲鱼","C++入门班"); Student student("迷途羔羊","C++入门班"); TeachingStudent teachingStudent("丁丁","丹丹","C++入门班","C++进阶版");// teacher.introduce(); teacher.teach(); student.introduce(); student.attendClass(); teachingStudent.introduce(); teachingStudent.teach(); teachingStudent.attendClass(); return 0;}
控制台打印结果:
大家好，我是小甲鱼，我教C++入门班.小甲鱼教C++入门班.大家好，我是迷途羔羊，我在C++入门班学习.迷途羔羊加入C++入门班学习。大家好，我是丹丹.我教C++入门班,同时我在C++进阶版学习.丁丁教C++入门班.丹丹加入C++进阶版学习。
这个时候，c++发明者为了解决这个问题，提供了“虚继承”（virtual inheritance）。
虚继承的语法：class Teacher : virtual public Person{...},这样做就解决了问题：让Student和Teacher类都虚继承自Person类，编译器将确保从Studnet何Teacher类再派生出来的子类只能拥有一份Person类的属性。
class Person{public: Person(std::string theName); void introduce(); protected: std::string name;};class Teacher : virtual public Person//虚继承，保证了只保留1份Person类的属性,实际上表明没有继承Person的属性{public: Teacher(std::string theName,std::string theClass); void teach(); void introduce(); protected: std::string classes;};class Student : virtual public Person//虚继承，保证了只保留1份Person类的属性,实际上表明没有继承Person的属性{public: Student(std::string theName,std::string theClass); void attendClass(); void introduce();protected: std::string classes;};Person::Person(std::string theName){ this->name = theName;}void Person::introduce(){ std::cout << "大家好，我是" << name << ".\n\n";}Teacher::Teacher(std::string theName,std::string theClass) : Person(theName){ this->classes = theClass;}void Teacher::teach(){ std::cout << this->name << "教" << classes << ".\n\n";}void Teacher::introduce(){ std::cout << "大家好，我是" << name << "，我教" << classes << ".\n\n";}Student::Student(std::string theName,std::string theClass) : Person(theName){ this->classes = theClass;}void Student::attendClass(){ std::cout << name << "加入" << classes << "学习。\n\n";}void Student::introduce(){ std::cout << "大家好，我是" << name << "，我在" << classes << "学习.\n\n";}class TeachingStudent : public Student,public Teacher{public: TeachingStudent(std::string theName,std::string classTeaching,std::string classAttending); void introduce();};TeachingStudent::TeachingStudent(std::string theName, std::string classTeaching, std::string classAttending):Teacher(theName,classTeaching),Student(theName,classAttending),Person(theName)//因为之前的Tearcher和Student都是虚继承，所以这里要再次继承于Person类的构造方法{ }void TeachingStudent::introduce(){ std::cout << "大家好，我是" << name << ".我教" << Teacher::classes << ",";//因为是虚继承，子类只保留1份属性，所以这里可以直接写name std::cout << "同时我在" << Student::classes << "学习.\n\n";}int main(int argc, const char * argv[]){ Teacher teacher("小甲鱼","C++入门班"); Student student("迷途羔羊","C++入门班"); TeachingStudent teachingStudent("丁丁","C++入门班","C++进阶版"); teacher.introduce(); teacher.teach(); student.introduce(); student.attendClass(); teachingStudent.introduce(); teachingStudent.teach(); teachingStudent.attendClass(); return 0;}
控制台打印结果：
大家好，我是小甲鱼，我教C++入门班.小甲鱼教C++入门班.大家好，我是迷途羔羊，我在C++入门班学习.迷途羔羊加入C++入门班学习。大家好，我是丁丁.我教C++入门班,同时我在C++进阶版学习.丁丁教C++入门班.丁丁加入C++进阶版学习。
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