stdmap - Adding element into C++ std::map inserts only one key -

i created simple library program, store map of book objects , quantity. add books map further able rent book, etc.

the problem in code, method called createlib inserts 1 book object map. why that? how solve this? doing wrong here? thanks.

#include <iostream> #include <string> #include <map>  using namespace std;  class author {     public:         string name;         author (){}         author(string n){name = n;} };  class book {     public:          author author;         string title;         static int id;          book (author a, string t){author = a, title = t; id ++;} };  int book::id = 0;  struct comapare {     bool operator() (const book& k1, const book& k2)     {         return k2.id < k1.id;     } };  class library {     public:         map<book, int, comapare> books;         void createlib()         {             author a1("bruce eckel");             book b1(a1, "thinking in java");             book b2(a1, "thinking in c++");              books.insert(std::make_pair(b1, 10));             books.insert(std::make_pair(b2, 2));              std::cout << books.size() << "\n";          } };  int main() {     library l;     l.createlib();      return 0; } 

edit:

here's working version:

#include <iostream> #include <string> #include <map>  using namespace std;  class author { public:     string name;     author () {}     author(string n)     {         name = n;     } };  class book { public:      author author;     string title;     static int id;     int rid;      book (author a, string t)     {         author = a, title = t;         id ++, rid = id;     } };  int book::id = 0;  struct comapare {     bool operator() (const book& k1, const book& k2)     {         return k2.rid < k1.rid;     } };  class library { public:     map<book, int, comapare> books;     void createlib()     {         author a1("bruce eckel");         book b1(a1, "thinking in java");         book b2(a1, "thinking in c++");          books.insert(std::make_pair(b1, 10));         books.insert(std::make_pair(b2, 2));          std::cout << books.size() << "\n";         ( std::map<book, int, comapare>::const_iterator iter = books.begin();                 iter != books.end(); ++iter )             cout << iter->first.title << "\t\t" << iter->second << '\n';      } };  int main() {     library l;     l.createlib();      return 0; } 

the problem id same instances of book class.

you need two id members: 1 static member increase, , 1 non-static member actual book id , assigned static id.