# days_alive.cpp

日数差と日数を使って、今日まで何日生きてきたかを計算してみる

    #include "boost/date_time/gregorian/gregorian.hpp"
    #include "boost/date_time/date_parsing.hpp"
    #include <iostream>

    int
    main()
    {

      using namespace boost::gregorian;
      std::string s;
      std::cout << "Enter birth day YYYY-MM-DD (eg: 2002-02-01): ";
      std::cin >> s;
      try {
        date birthday(boost::date_time::parse_date<date>(s));
        // 誕生日(2002年1月1日);

        date today = day_clock::local_day();
        date_duration days_alive = today - birthday;
        date_duration one_day(1);
        if (days_alive == one_day) {
          std::cout << "Born yesterday, very funny" << std::endl;
        }
        else if (days_alive <
          std::cout << "Not born yet, hmm: " << days_alive.days()
              << " days" <<std::endl;
        }
        else {
          std::cout << "Days alive: " << days_alive.days() << std::endl;
        }

      }
      catch(...) {
        std::cout << "Bad date entered: " << s << std::endl;
      }
      return 0;
    };