boost::posix_time 时间处理

1.当前起始时间（microsec微秒级别）
boost::posix_time::ptime start_time = boost::posix_time::microsec_clock::local_time();
2.当前结束时间
boost::posix_time::ptime end_time = boost::posix_time::microsec_clock::local_time();
3.时间差
boost::posix_time::time_duration td = end_time - start_time;