const 与mutable

#include <iostream>
using namespace std;

class Student{
public:
    void Register()const {
        m_register = true;
    }
private:
    bool m_register;
};

int main(int argc, char **argv)
{
    Student *s = new Student();
    s->Register();
    return 0;
}

错误，因为Register()被const修饰，但是修改了成员变量m_register

1.cpp: In member function ‘void Student::Register() const’:
1.cpp:8:22: error: assignment of member ‘Student::m_register’ in read-only object

解决方法：
为了突破const的限制，使用mutable关键字，允许const修饰的函数允许修改被mutable修饰的成员变量

#include <iostream>
using namespace std;

class Student{
public:
    void Register()const {
        m_register = true;
    }
private:
    mutable bool m_register;//mutable
};

int main(int argc, char **argv)
{
    Student *s = new Student();
    s->Register();
    return 0;