boost 日期时间计算

示例代码如下：

 #include <boost/date_time/gregorian/gregorian.hpp>
 #include <boost/date_time/posix_time/posix_time.hpp>
 using namespace boost::gregorian;
 using namespace boost::posix_time;
 #include <iostream>
 using namespace std;
 #include <string>

 void TimerTest()
 {
     {
         // 例1. 日期计算：打印今天日期；今年感恩节（11月的第4个星期四）的日期；如果还没有到今年感恩节，打印今天到感恩节还有多少天;
         typedef nth_day_of_the_week_in_month nth_dow;
         date today = day_clock::local_day(); // today; // 获取今天日期;
         std::cout << "today is: " << today << std::endl;
         nth_dow fourth_thur_in_nov(nth_dow::fourth, Thursday, Nov); // 4th thursday in Nov;
         date thanksgiving = fourth_thur_in_nov.get_date(today.year()); // get the date this year;
         std::cout << "Thanksgiving day this year is: " << thanksgiving << std::endl;
         if(today < thanksgiving)
         {
             date_duration dd = thanksgiving - today; // date duration; // 时间差;
             std::cout << "has " << dd.days() << " days to thanksgiving."<< std::endl;
         }
     }

     {
         // 日期操作;
         std::cout << std::endl << std::endl;
         date today = day_clock::local_day();                        // today; // 获取今天日期;
         std::cout << today.year() << std::endl;                        // 打印年;
         std::cout << today.month() << std::endl;                    // 打印月;
         std::cout << today.day() << std::endl;                        // 打印日;
         std::cout << today.week_number() << std::endl;                // 今年的第几周;
         std::cout << today.day_of_week() << std::endl;                // 打印星期几;
         std::cout << today.day_of_year() << std::endl;                // 打印一年中的第几天;
         std::cout << today.end_of_month() << std::endl;                // 打印本月的最后一天是，闰月的2月，可以试试;
         std::cout << today.modjulian_day() << std::endl;
         std::cout << today.julian_day() << std::endl;
         std::cout << (today.day_of_week() == ) << std::endl;        // 判断今天是星期日吗，周日为0;
         std::cout << (today.end_of_month() == today) << std::endl;    // 判断今天是当月的最后一天吗;
         date dateTemp = from_string("2016-11-26");
         date_duration dd = dateTemp - today;                        // 时间差;
         std::cout << "subDate = " << dd.days() << std::endl;        // 相差多少天;
         // 获取指定（11月的第4个星期四）日期;
         typedef nth_day_of_the_week_in_month nth_dow;
         nth_dow fourth_thur_in_nov(nth_dow::fourth, Thursday, Nov);        // 4th thursday in Nov;
         date thanksgiving = fourth_thur_in_nov.get_date(today.year());    // get the date this year;
     }

     {
         // 时间操作;
         ptime timeTemp = second_clock::local_time();                    // 获取当前时间，秒级别;
         std::cout << timeTemp.time_of_day() << std::endl;                // 当前时间;
         std::cout << timeTemp.date() << std::endl;                        // 当前时间对应的日期;
         ptime destTime = time_from_string("2016-06-15 17:00:00");
         time_duration tt = timeTemp - destTime;                            // 时间差;
         std::cout << "subTime = " << (tt.seconds() >= ) << std::endl;    // 相差多少秒;
     }
 }