我們知道在Java中是自動實現(xiàn)多態(tài)的，Java中規(guī)定重寫的方法的訪問權(quán)限不能縮小。那么在C++中我們實現(xiàn)多態(tài)的時候是否可以更改（縮小）訪問權(quán)限呢？

經(jīng)過測試，得到的答案如下：如果用基類指針指向派生類對象實現(xiàn)多態(tài)則虛函數(shù)的訪問權(quán)限以基類中的訪問權(quán)限為準。因此只要基類中的訪問權(quán)限是public就可以訪問。派生類對象的訪問權(quán)限以派生類中的為準。

這就意味這我們只要基類的虛函數(shù)權(quán)限是public，我們就可以使用基類指針訪問到派生類私有的虛函數(shù)。

具體樣例：

#include<cstdio> #include<iostream> #include<string>using namespace std;class Employee { protected:string name, ID;Employee(string _name,string _ID):name(_name),ID(_ID){}void SetName(string _name){name = _name;}void SetID(string _ID){ID = _ID;}string GetName(){return name;}string GetID(){return ID;} public:virtual double DisplaySalary(){return 0;}virtual void DisplayInform() = 0; };class Manager :public Employee {double salary; public:Manager(string _name,string _ID,double _salary=5000):Employee(_name,_ID),salary(_salary){}double DisplaySalary(){return salary;}void DisplayInform(){cout << "經(jīng)理信息：" << endl;cout << "姓名：" << name << "\tID:" << ID << "\t薪資：" << salary << endl;}void SetSalary(double _salary){salary = _salary;} };class Technician :public Employee {double wage, hours; public:Technician(string _name, string _ID, double _wage = 100,double _hours=288):Employee(_name,_ID),wage(_wage),hours(_hours){}void SetWage(double _wage){wage = _wage;}void SetHours(double _hours){hours = _hours;}double DisplayWage(){return wage;}double DisplayHours(){return hours;} private:double DisplaySalary(){return wage * hours;}void DisplayInform(){cout << "經(jīng)理信息：" << endl;cout << "姓名：" << name << "\tID:" << ID << "\t薪資：" << DisplaySalary() << endl;} };int main() {Employee* p1 = new Manager("A", "01", 9000);Employee* p2 = new Technician("B", "02");Technician C("C", "03");p1->DisplayInform();p2->DisplayInform();cout << C.Employee::DisplaySalary() << endl;//直接訪問會報錯p2 = &C;cout << p2->DisplaySalary() << endl;return 0; }

運行結(jié)果：

總結(jié)

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