当有类中有const限制的常量时 再自定义拷贝函数为什么可以重载

例如：

#include <string>

using namespace std;

class teacher

{

public:

//**********构造函数声明*****构造函数无返回值*******//

teacher(string name="ames",int age=18,int m=100);

teacher (const teacher &tea,int m);

teacher (const teacher &tea,int m ,int n);

void setname(string _name);

string getname();

void setgender(string _gender);

string getgender();

void setage(int _age);

int getage();

int getstudent();

void teach();

private:

string m_strName;

string m_strGender;

int m_iAge;

const int m_iStudent;

};