In file included from main.cpp:16:0:
date.h: In constructor 'Date::Date(int, int, int)':
date.h:10:9: error: 'Date::y' will be initialized after [-Werror=reorder]
     int y;
         ^
date.h:9:9: error:   'int Date::m' [-Werror=reorder]
     int m;
         ^
date.h:12:5: error:   when initialized here [-Werror=reorder]
     Date(int year, int month, int day) : y(year), m(month), d(day) {
     ^~~~
date.h:9:9: error: 'Date::m' will be initialized after [-Werror=reorder]
     int m;
         ^
date.h:8:9: error:   'int Date::d' [-Werror=reorder]
     int d;
         ^
date.h:12:5: error:   when initialized here [-Werror=reorder]
     Date(int year, int month, int day) : y(year), m(month), d(day) {
     ^~~~
cc1plus: all warnings being treated as errors