【C++】【学习笔记】【029】虚继承

Myth丶恋晨 2022-08-06 01:26 187阅读 0赞

**引入原因**：在多继承的时候，会出现基类的多重拷贝。如上一节的示例中，Teacher类和Student类都继承自Person类，那么在TeachingStudent类进行多继承的时候，会有两份Person类的成员name。为解决该问题，则引入了虚继承的概念。

**基本语法**：

class Teacher : virtual public Person
    
    { … }

**样例（非虚继承）**：

#include <iostream>
    #include <string>
    
    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;
    };
    
    class TeachingStudent : public Student, public Teacher 
    {
    public:
        TeachingStudent(std::string theName1, std::string theName2, std::string classTeaching, std::string classAttending);
    
        void introduce();
    };
    
    Person::Person(std::string theName)
    {
        name = theName;
    }
    
    void Person::introduce()
    {
        std::cout << "Hello, I'm " << name << ".\n\n";
    }
    
    Teacher::Teacher(std::string theName, std::string theClass) : Person(theName)
    {
        classes = theClass;
    }
    
    void Teacher::teach()
    {
        std::cout << name << " teach " << classes << ".\n\n";
    }
    
    void Teacher::introduce()
    {
        std::cout << "Hello, I'm " << name << ". I teach " << classes << ".\n\n";
    }
    
    Student::Student(std::string theName, std::string theClass) : Person(theName)
    {
        classes = theClass;
    }
    
    void Student::attendClass()
    {
        std::cout << name << " join " << classes << " to study.\n\n";
    }
    
    void Student::introduce()
    {
        std::cout << "Hello, I'm " << name << ". I'm studing at " << classes << ".\n\n";
    }
    
    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 << "Hello, I'm " << Student::name << ". I teach " << Teacher::classes << ", ";
        std::cout << "and I study at " << Student::classes << ".\n\n";
    }
    
    int main()
    {
        Teacher teacher("Turtle", "C++ class");
        Student student("Sheep", "C++ class");
        TeachingStudent teachingStudent("Ding", "Dan", "C++ class", "C++ high level class");
    
        teacher.introduce();
        teacher.teach();
        student.introduce();
        student.attendClass();
        teachingStudent.introduce();
        teachingStudent.teach();
        teachingStudent.attendClass();
    
        return 0;
    }

结果：

Hello, I'm Turtle. I teach C++ class.
    
    Turtle teach C++ class.
    
    Hello, I'm Sheep. I'm studing at C++ class.
    
    Sheep join C++ class to study.
    
    Hello, I'm Dan. I teach C++ class, and I study at C++ high level class.
    
    Ding teach C++ class.
    
    Dan join C++ high level class to study.

**样例（虚继承）**：

#include <iostream>
    #include <string>
    
    class Person
    {
    public:
        Person(std::string theName);
    
        void introduce();
    
    protected:
        std::string name;
    };
    
    class Teacher : virtual public Person
    {
    public:
        Teacher(std::string theName, std::string theClass);
    
        void teach();
        void introduce();
    
    protected:
        std::string classes;
    };
    
    class Student : virtual public Person
    {
    public:
        Student(std::string theName, std::string theClass);
    
        void attendClass();
        void introduce();
    
    protected:
        std::string classes;
    };
    
    class TeachingStudent : public Student, public Teacher 
    {
    public:
        TeachingStudent(std::string theName, std::string classTeaching, std::string classAttending);
    
        void introduce();
    };
    
    Person::Person(std::string theName)
    {
        name = theName;
    }
    
    void Person::introduce()
    {
        std::cout << "Hello, I'm " << name << ".\n\n";
    }
    
    Teacher::Teacher(std::string theName, std::string theClass) : Person(theName)
    {
        classes = theClass;
    }
    
    void Teacher::teach()
    {
        std::cout << name << " teach " << classes << ".\n\n";
    }
    
    void Teacher::introduce()
    {
        std::cout << "Hello, I'm " << name << ". I teach " << classes << ".\n\n";
    }
    
    Student::Student(std::string theName, std::string theClass) : Person(theName)
    {
        classes = theClass;
    }
    
    void Student::attendClass()
    {
        std::cout << name << " join " << classes << " to study.\n\n";
    }
    
    void Student::introduce()
    {
        std::cout << "Hello, I'm " << name << ". I'm studing at " << classes << ".\n\n";
    }
    
    TeachingStudent::TeachingStudent(std::string theName,
                                     std::string classTeaching,
                                     std::string classAttending)
                                     : Teacher(theName, classTeaching), Student(theName, classAttending), Person(theName)
    {
    }
    
    void TeachingStudent::introduce()
    {
        std::cout << "Hello, I'm " << name << ". I teach " << Teacher::classes << ", ";
        std::cout << "and I study at " << Student::classes << ".\n\n";
    }
    
    int main()
    {
        Teacher teacher("Turtle", "C++ class");
        Student student("Sheep", "C++ class");
        TeachingStudent teachingStudent("Ding", "C++ class", "C++ high level class");
    
        teacher.introduce();
        teacher.teach();
        student.introduce();
        student.attendClass();
        teachingStudent.introduce();
        teachingStudent.teach();
        teachingStudent.attendClass();
    
        return 0;
    }

结果：

Hello, I'm Turtle. I teach C++ class.
    
    Turtle teach C++ class.
    
    Hello, I'm Sheep. I'm studing at C++ class.
    
    Sheep join C++ class to study.
    
    Hello, I'm Ding. I teach C++ class, and I study at C++ high level class.
    
    Ding teach C++ class.
    
    Ding join C++ high level class to study.