目录
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)
class Student{
public:
int score;
virtual void study(){
cout<<"Student::study()"<<endl;
}
Student(){
cout<<"Student:Student"<<endl;
}
Student(int score){
cout<<"Student:Student(int score)"<<endl;
this->score = score;
}
};
class Worker{
public:
int salary;
virtual void work(){
cout<<"Worker::work()"<<endl;
}
Worker(){
cout<<"Worker::Worker"<<endl;
}
Worker(int salary){
cout<<"Worker::Worker(int salary)"<<endl;
this->salary = salary;
}
};
class Undergraduate:public Student,public Worker{
public:
int grade;
void play(){
cout<<"Undergraduate::play()"<<endl;
}
Undergraduate(){
cout<<"Undergraduate:Undergraduate"<<endl;
}
Undergraduate(int grade){
cout<<"Undergraduate:Undergraduate(int grade)"<<endl;
this->grade = grade;
}
};
void mutiInheritUsing(){
Undergraduate * grade = new Undergraduate(4);
grade->score = 100;
grade->salary = 1000;
grade->grade = 4;
grade->study();
grade->work();
grade->play();
delete grade;
}
多继承体系下的构造函数调用
见上边类的继承关系
多继承-虚函数
如果子类继承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
void multiVirtualUsing(){
Undergraduate * grade = new Undergraduate();
grade->score = 100;
grade->salary = 1000;
grade->grade = 4;
cout<<"sizeof(Undergraduate)"<<sizeof(Undergraduate)<<endl;
/**
(lldb) po grade
0x0000000100505160
(lldb) memory read/4xg 0x0000000100505160
虚表一的地址 变量score的值
0x100505160: 0x000000010001e328 0x0000000000000064
虚表二的地址 变量salary和变量grade的值
0x100505170: 0x000000010001e340 0x00000004000003e8
*/
}
同名函数、同名成员变量
class Animal{
public:
int age;
void eat(){
cout<<"Animal::eat()"<<endl;
}
};
class Quan{
public:
int age;
void eat(){
cout<<"Quan::eat()"<<endl;
}
};
class Dog:public Animal,public Quan{
public:
int age;
void eat(){
cout<<"Dog::eat()"<<endl;
}
};
void multiFunAndMemeberVar(){
Dog * dog = new Dog();
//同名函数
dog->Dog::eat();
dog->Quan::eat();
dog->Animal::eat();
dog->eat();
//同名的成员变量
dog->age = 10;
dog->Animal::age = 8;
dog->Quan::age = 9;
cout<<"dog->Dog::age is "<<dog->Dog::age<<endl;
cout<<"dog->Animal::age is "<<dog->Animal::age<<endl;
cout<<"dog->Quan::age is "<<dog->Quan::age<<endl;
cout<<"dog->age is "<<dog->age<<endl;
delete dog;
}
菱形继承
class Person{
public:
int age;
};
class Student:public Person{
public:
int score;
};
class Worker:public Person{
public:
int salary;
};
class Undergraduate:public Student,public Worker{
public:
int grade;
};
void lingxingInheritUsing(){
Undergraduate * grade = new Undergraduate();
cout<<"sizeof(Undergraduate)"<<sizeof(Undergraduate)<<endl;
//直接这么写有二义性
// grade->age = 10;
grade->Student::age = 10;
grade->Worker::age = 11;
}
虚继承
虚继承可以解决菱形继承带来的问题 Person类被称为虚基类
class Person1{
public:
int age;
};
class Student1:virtual public Person1{
public:
int score;
};
class Worker1:virtual public Person1{
public:
int salary;
};
class Undergraduate1:public Student1,public Worker1{
public:
int grade;
};
void virtualInheritUsing(){
Undergraduate1 * grade = new Undergraduate1();
cout<<"sizeof(Undergraduate1)"<<sizeof(Undergraduate1)<<endl;
//此处不会产生二义性
grade->age = 10;
}
多继承的应用
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 {
public:
void clean() {
}
void cook() {
}
};
class SuperStudent : public JobBaomu, public JobTeacher {
public:
void clean() {
}
void cook() {
}
void playBaseball() {
}
void playFootball() {
}
};
void multyInheritApplyUsing(){
SuperStudent * spuStu = new SuperStudent();
spuStu->cook();
delete spuStu;
}
行者常至，为者常成！