[Boost]boost的时间和日期处理-（2）时间的操作

<开篇>

本篇紧接着boost上篇叙述Boost::DateTime的时间处理。在C++中，常见的时间有time_t, FILETIME和tm，而boost中用ptime。

构造ptime

1.ptime的构造函数有四种：

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构造

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

5:  ptime pt2(p1);//拷贝构造函数

6:  ptime pt3(neg_infin);//特殊值构造

7:  ptime p;//默认构造函数，这里p等于not_a_date_time

2.用string构造ptime:

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

2:  ptime pt1(time_from_string(ts1));

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

4:  ptime pt2(from_iso_string(ts2));

5:  

3.通过时钟构造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构造ptime:

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

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

ptime访问日期时间

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转换为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与tm，time_t，FILETIME互转

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:  

对于这两者的区别，一个是时间间隔，一个是时间起止的一个窗口。time_duration用于ptime的时间偏移计算为主。而time_period可以计算一个ptime时间点是否在这个时间区间内(参考contains函数)。time_period在创建之后可以扩展，可以平移，函数分别为expand和shift。请大家自己细究。

下一篇将介绍关于boost.datetime的格式化输入输出。

<完结>