Hi All, Since I posted the previous message, I made some experiments. First, I changed the employee from struct to class: From struct employee { int id; std::string name; int age; employee(int id_,std::string name_,int age_):id(id_),name(name_),age(age_){} friend std::ostream& operator<<(std::ostream& os,const employee& e) { os<, ordered_non_unique< tag<name>,BOOST_MULTI_INDEX_MEMBER(employee,std::string,name)>, ordered_non_unique< tag<age>, BOOST_MULTI_INDEX_MEMBER(employee,int,age)> >

employee_set;

So, I had to change the scope of index class members to public, and it worked: class employee { public: int id; std::string name; int age; employee(int id_,std::string name_,int age_):id(id_),name(name_),age(age_){} friend std::ostream& operator<<(std::ostream& os,const employee& e) { os<