C++快速入門---虛繼承（21）

通過虛繼承某個基類，就是在告訴編譯器，從當前這個類再派生出來的子類只能擁有那個基類的一個例項。

虛繼承的語法：

class Teacher : virtual public Person

{ ... }

讓Student類和Teacher類都虛繼承自Person類，編譯器將確保從Student和Teacher類再派生出來的子類只能擁有一份Person類的屬性。

程式碼如下：

#include <iostream>
#include <string>

class Person
{
public:
	Person(std::string theName);
	
	void introduce();
	
protected:
	std::string name;
};

//虛繼承
class Teacher : virtual public Person
{
public:
	Teacher(std::string theName, std::string theClass);
	
	void teach();
	void introduce();

protected:
	std::string classes;
};

//虛繼承
class Student : virtual public Person
{
public:
	Student(std::string theName, std::string theClass);
	
	void attendClass();
	void introduce();

protected:
	std::string classes;
};

//助教 
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 << "大家好，我是" << name << ".\n\n";
}

Teacher::Teacher(std::string theName, std::string theClass) : Person(theName)
{
	classes = theClass;
}

void Teacher::teach()
{
	std::cout << 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)
{
	classes = theClass;
}

void Student::attendClass()
{
	std::cout << name << "加入" << classes << "學習.\n\n";
}

void Student::introduce()
{
	std::cout << "大家好,我是" << name << ",我在" << classes << "學習.\n\n";
}

//因為Teacher和Student都是虛繼承,不能擁有Person類的拷貝(備份),所以需要呼叫Person的構造方法 
TeachingStudent::TeachingStudent(std::string theName,
								 std::string classTeaching,
								 std::string classAttending)
								 : 
								 Teacher(theName, classTeaching), 
								 Student(theName, classAttending),
								 Person(theName)
{
}

void TeachingStudent::introduce()
{
	std::cout << "大家好,我是" << name << ".我教" << Teacher::classes << ",";
	std::cout << "同時我在" << Student::classes << "學習.\n\n";
}

int main()
{
	Teacher teacher("小甲魚", "C++入門班");
	Student student("迷途羔羊", "C++入門班");
	TeachingStudent teachingStudent("丁丁", "C++入門班", "C++進階版"); 
	
	teacher.introduce();
	teacher.teach();
	student.introduce();
	student.attendClass();
	teachingStudent.introduce();
	teachingStudent.teach();
	teachingStudent.attendClass();
	
	return 0;
}