private,protected,public

private

• 所有的data尽量用private属性

父类不能访问子类的private属性

有如下程序:

#include <iostream>#include <string>using namespace std;class Person{private:    string name;public:    void print();    Person(string aname):name("hello"){}};void Person::print() {    cout << "Person's name is " << name << endl;}class A {private:    int i;    Person man;public:    A():i(0),man("12"){cout << "A(), i = " << i << endl;}    ~A(){cout << "~A(), i = " << i << endl;}    void print();};void A::print() {    cout << "man's name is " << man.name << endl; //Error - 'name' is a private member of 'Person'}int main(){    A a;    a.print();    return 0;}

所以，即使一个对象包含了另一个对象，父对象也不能访问子对象的private属性。

protected

• 只有parent和child可以访问
• 一般用于设计一些只有parent和child可以访问的接口

public

• 都可以访问