C++-面向对象(六)
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本文链接：https://blog.csdn.net/weixin_42528266/article/details/102753332
虚析构函数
- 含有虚函数的类，应该将析构函数声明为虚函数（虚析构函数）
- delete父类指针时，才会调用子类的析构函数，保证析构的完整性
#include <iostream>
using namespace std;
class Animal {
public:
int m_age;
virtual void speak() {
cout << "Animal::speak()" << endl;
}
virtual void run() {
cout << "Animal::run()" << endl;
}
virtual ~Animal() {
cout << "~Animal()" << endl;
}
};
class Cat : public Animal {
public:
int m_life;
Cat() :m_life(0) {}
void speak() {
cout << "Cat::speak()" << endl;
}
void run() {
cout << "Cat::run()" << endl;
}
~Cat() {
cout << "~Cat()" << endl;
}
};
int main() {
Animal *cat1 = new Cat();
cat1->speak();
cat1->run();
delete cat1;
getchar();
return 0;
}纯虚函数
- 纯虚函数：没有函数体且初始化为0的虚函数，用来定义接口规范
- 抽象类（Abstract Class） 含有纯虚函数的类，不可以实例化（不可以创建对象）
- 抽象类也可以包含非纯虚函数
- 如果父类是抽象类，子类没有完全实现纯虚函数，那么这个子类依然是抽象类
#include <iostream>
using namespace std;
// 类似于Java中接口、抽象类
// 类似于OC中的协议protocol
// Animal是个抽象类
class Animal {
public:
virtual void speak() = 0;
virtual void run() = 0;
};
class Cat : public Animal {
public:
void run() {
}
};
class WhiteCat : public Cat {
public:
void speak() {
}
void run() {
}
};
int main() {
Cat *cat = new WhiteCat();
getchar();
return 0;
}多继承
- C++允许一个类可以有多个父类（不建议使用，会增加程序设计复杂度）
#include <iostream>
using namespace std;
class Student {
public:
int m_score;
Student(int score = 0) :m_score(score) { }
void study() {
cout << "Student::study() - score = " << m_score << endl;
}
~Student() {
cout << "~Student" << endl;
}
};
class Worker {
public:
int m_salary;
Worker(int salary = 0) :m_salary(salary) { }
void work() {
cout << "Worker::work() - salary = " << m_salary << endl;
}
~Worker() {
cout << "~Worker" << endl;
}
};
class Undergraduate : public Student, public Worker {
public:
int m_grade;
Undergraduate(
int score = 0,
int salary = 0,
int grade = 0) :Student(score), Worker(salary), m_grade(grade) {
}
void play() {
cout << "Undergraduate::play() - grade = " << m_grade << endl;
}
~Undergraduate() {
cout << "~Undergraduate" << endl;
}
};
int main() {
{
Undergraduate ug;
ug.m_score = 100;
ug.m_salary = 2000;
ug.m_grade = 4;
ug.study();
ug.work();
ug.play();
}
cout << sizeof(Undergraduate) << endl;
getchar();
return 0;
}多继承体系下的构造函数调用
#include <iostream>
using namespace std;
class Student {
public:
virtual void study() {
cout << "Student::study()" << endl;
}
};
class Worker {
public:
virtual void work() {
cout << "Worker::work()" << endl;
}
};
class Undergraduate : public Student, public Worker {
public:
void study() {
cout << "Undergraduate::study()" << endl;
}
void work() {
cout << "Undergraduate::work()" << endl;
}
void play() {
cout << "Undergraduate::play()" << endl;
}
};
int main() {
/*Undergraduate ug;
ug.study();
ug.work();
ug.play();*/
Student *stu = new Undergraduate();
stu->study();
Worker *worker = new Undergraduate();
worker->work();
cout << sizeof(Undergraduate) << endl;
getchar();
return 0;
}多继承-虚函数
- 如果子类继承的多个父类都有虚函数，那么子类对象就会产生对应的多张虚表
同名函数
#include <iostream>
using namespace std;
class Student {
public:
int m_age;
};
class Worker {
public:
int m_age;
};
class Undergraduate : public Student, public Worker {
public:
int m_age;
};
int main() {
Undergraduate ug;
ug.m_age = 10;
ug.Student::m_age = 20;
ug.Worker::m_age = 30;
ug.Undergraduate::m_age = 40;
cout << sizeof(Undergraduate) << endl;
getchar();
return 0;
}
//class Student {
//public:
// void eat() {
// cout << "Student::eat()" << endl;
// }
//};
//
//class Worker {
//public:
// void eat() {
// cout << "Worker::eat()" << endl;
// }
//};
//
//class Undergraduate : public Student, public Worker {
//public:
// void eat() {
// cout << "Undergraduate::eat()" << endl;
// }
//};
//
//int main() {
// Undergraduate ug;
// ug.eat();
// ug.Worker::eat();
// ug.Student::eat();
// ug.Undergraduate::eat();
//
// getchar();
// return 0;
//}菱形继承
- 菱形继承带来的问题
- 最底下子类从基类继承的成员变量冗余、重复
- 最底下子类无法访问基类的成员，有二义性
#include <iostream>
using namespace std;
// 非虚继承：(10 + 10 + 3) * 4 = 23 * 4
// 虚继承：(10 + 2 + 2 + 1) * 4 = 15 * 4
class Person {
public:
int m_age;
int m_age1;
int m_age2;
int m_age3;
int m_age4;
int m_age5;
int m_age6;
int m_age7;
int m_age8;
int m_age9;
};
class Student : virtual public Person {
public:
int m_score;
};
class Worker : virtual public Person {
public:
int m_salary;
};
class Undergraduate : public Student, public Worker {
public:
int m_grade;
};
int main() {
/*Undergraduate ug;
ug.m_grade = 10;
ug.m_score = 20;
ug.m_salary = 20;*/
cout << sizeof(Student) << endl;
getchar();
return 0;
}虚继承
- 虚继承可以解决菱形继承带来的问题
#include <iostream>
using namespace std;
// 多继承：增加程序的复杂度
// 多继承有一个很好的用途：
// 一个类实现多个接口（Java）
// 一个类遵守多份协议（OC）
// 一个类继承多个抽象类（C++）
class JobBaomu {
virtual void clean() = 0;
virtual void cook() = 0;
};
class JobTeacher {
virtual void playBaseball() = 0;
virtual void playFootball() = 0;
};
class SalesMan : public JobBaomu {
void clean() {
}
void cook() {
}
};
class Student : public JobBaomu, public JobTeacher {
void clean() {
}
void cook() {
}
void playBaseball() {
}
void playFootball() {
}
};
int main() {
// 兼职中心
// 招聘一些人来做兼职
// 兼职的岗位很多种（保姆、老师、开挖掘机）
// 应聘的人种类也很多（学生、XXX）
getchar();
return 0;
}本文参与 腾讯云自媒体同步曝光计划，分享自作者个人站点/博客。
原始发表：2019/10/26 ，如有侵权请联系 cloudcommunity@tencent.com 删除
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