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<開篇>

本篇緊接著boost上篇敘述Boost::DateTime的時間處理。在C++中，常見的時間有time_t, FILETIME和tm，而boost中用ptime。

構造ptime

1.ptime的構造函數有四種：

1:      using namespace boost::posix_time;

2:      using namespace boost::gregorian;

3:  ptime pt(date(2013,Jan,24),time_duration(1,2,3)); //由date和time_duration構造

4:  ptime pt1(date(2013,Jan,24),hours()+nanosec(5));//改變形式的time_duration也能使用

5:  ptime pt2(p1);//拷貝構造函數

6:  ptime pt3(neg_infin);//特殊值構造

7:  ptime p;//默認構造函數，這里p等于not_a_date_time

2.用string構造ptime:

1:      std::string ts1("2013-01-30 23:32:22.000");//固定格式，小數點后支持6位

2:  ptime pt1(time_from_string(ts1));

3:  std::string ts2("20130130T233222");//沒有分隔符的date和time

4:  ptime pt2(from_iso_string(ts2));

5:  

3.通過時鐘構造ptime:

1:      ptime ct1(second_clock::local_time());

2:  ptime ct2(second_clock::universal_time());

3:  ptime ct3(microsec_clock::local_time());

4:  ptime ct4(microsec_clock::universal_time());

5:  

4.time_t和FILETIME構造ptime:

1:      ptime t = from_time_t(tt); // 其中tt為time_t

2:  ptime t1 = from_ftime<ptime>(ft); //其中ft為FILETIME

ptime訪問日期時間

1:      using namespace boost::posix_time;

2:      using namespace boost::gregorian;

3:  ptime now(second_clock::local_time());

4:  std::cout << "today is: " << now.date() << std::endl;

5:  std::cout << "time is: " << now.time_of_day() << std::endl;

6:  

ptime轉換為string

1:      std::string now_str(to_simple_string(now));

2:  std::string now_iso_str(to_iso_string(now));

3:  std::string now_iso_ext_str(to_iso_extended_string(now));

4:  std::cout << now_str << std::endl;

5:  std::cout << now_iso_str << std::endl;

6:  std::cout << now_iso_ext_str << std::endl;

ptime與tm，time_t，FILETIME互轉

1.tm

 1:     using namespace boost::posix_time;

 2:     using namespace boost::gregorian;

 3:     tm pt_tm;

 4:     pt_tm.tm_year = 113;

 5:     pt_tm.tm_mon = 11;

 6:     pt_tm.tm_mday = 25;

 7:     pt_tm.tm_hour = 2;

 8:     pt_tm.tm_min = 23;

 9:     pt_tm.tm_sec = 40;

10:  

11:     ptime pt = data_from_tm(pt_tm);

12:     std::cout << pt << std::endl;

13:  

14:     pt = pt + hours(2);

15:     tm pt_tm1 = to_tm(pt);

2. time_t

 1:      using namespace boost::posix_time;

 2:      using namespace boost::gregorian;

 3:  

 4:  time_t now = time(NULL);

 5:  std::cout << "time_t : " << now << std::endl;

 6:  ptime now_pt = from_time_t(now);

 7:  std::cout << "ptime from time_t : " << now_pt.time_of_day() << std::endl;

 8:  tm* now_tm = gmtime(&now);

 9:  std::cout << "tm struct: hour : " << now_tm->tm_hour << std::endl;

10:  

3.FILETIME

1:      FILETIME ft;

2:  ft.dwHighDateTime = 29715317;

3:  ft.dwLowDateTime = 3865122988UL

4:      ptime pt = from_ftime<ptime>(ft);

5:  // pt ===> 2005-Jun-07 15:30:57.03958200

6:  

time_duration和time_period

 1:      using namespace boost::posix_time;

 2:      using namespace boost::gregorian;

 3:  

 4:  time_duration td(100,200,3,9);

 5:  std::cout << td << std::endl;

 6:  date d(2013,Feb,5);

 7:  ptime pt(d,minutes(10));

 8:  ptime pt1(d,hours(10));

 9:  time_period tp(pt,pt1);

10:  std::cout << tp << std::endl;

11:  

對于這兩者的區別，一個是時間間隔，一個是時間起止的一個窗口。time_duration用于ptime的時間偏移計算為主。而time_period可以計算一個ptime時間點是否在這個時間區間內(參考contains函數)。time_period在創建之后可以擴展，可以平移，函數分別為expand和shift。請大家自己細究。

下一篇將介紹關于boost.datetime的格式化輸入輸出。

<完結>

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