标准：：字符串>>：字符串没有运算符">>"

我遇到了问题，我不知道如何解决。

这是我制作的搜索功能，我从中收到错误;

void guestSearch()
{
    &Reservation::getfirstName;
    &Reservation::getlastName;
    &Date::getday;
    &Date::getmonth;
    &Date::getyear;
    Hotelreservation reg;
    reg.duration;
    reg.occupants;
    &Contact::getareaCode;
    &Contact::getexchange;
    &Contact::getline;
    system("cls");
    cout<<"Enter Line Number for the Guest you are searching for:";
    cin>>line;
    string line2= to_string(line);
    line2.append(".txt");
    ifstream filemain(line2);
    while(firstName>>lastName>>day>>month>>year>>duration>>occupants>>areaCode>>exchange>>line)
    {
        int firstNameLength=firstName.size();
        int lastNameLength=lastName.size();
        int lengthTotal=firstName+lastName;
        string result;
        cout<< "Is this the correct Guest (y/n)"<<endl;
        cout<<"Name"<<firstName<<" "<<lastName<<end;
        cin>>result;
        if(result=="y")
        {
            system("cls");
            cout<<"Name";
            for(int y = 1; y<lengthTotal; y++)
            {
                cout<< " ";
            }
            cout<<"Reservation Date";
            for(int z=1; z<2; z++)
            {
                cout<< " ";
            }
            cout<<"Duration of Stay";
            for(int x=1; x<2; x++)
            {
                cout<< " ";
            }
            cout<<"Occupants";
            for(int u=1; u<2; u++)
            {
                cout<< " ";
            }
            cout<<"Contact Number";
            for(int v=1; v<2; v++)
            {
                cout<< " ";
            }
        }
        cout<<"Date Reservation was made:"<<day<<"/"<<month<<"/"<<year<<endl;
        cout<<"Duration Of Stay:"<<duration<<endl;
        cout<<"Occupants:"<<occupants<<endl;
        cout<<"Contact Number:"<<areaCode<<"-"<<exchange<<"-"<<line<<endl;
    }
}

我在firstName ">>"后的while声明中收到错误，我得到这个：

智能感知：没有运算符">>"匹配这些操作数，操作数类型为：std：：string>>std：：string"