chrono

C++11 STL Boost

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chrono::duration

template <class Rep, class Period = ratio<1> >
class duration;

chrono是一个time library, 源于boost。其所有实现均在std::chrono namespace下
　　Rep表示一种数值类型，用来表示Period的数量，比如int float double
Period是ratio类型，用来表示[用秒表示的时间单位]比如seconds miliseconds
常用的duration<Rep,Period>已经定义好了，在std::chrono::duration下：

ratio	Period
ratio<3600, 1>	hours
ratio<60, 1>	minutes
ratio<1, 1>	seconds
ratio<1, 1000>	microseconds
ratio<1, 1000000>	microseconds
ratio<1, 1000000000>	nanosecons

typedef duration < , ratio<3600,1> > hours;
typedef duration < , ratio<60,1> > minutes;
typedef duration < , > seconds;
typedef duration < , milli > milliseconds;//milli (i.e., ratio<1,1000>)
typedef duration < , micro > microseconds;//micro (i.e., ratio<1,1000000>)
typedef duration < , nano > nanoseconds; //nano (i.e., ratio<1,1000000000>)

example

chrono::time_point

template <class Clock, class Duration = typename Clock::duration>
class time_point;

　　time_point，是C++11引入的表示特定时间点的工具。

std::chrono::time_point<Clock,Duration>常用的具体类型：
std::chrono::time_point<std::chrono::system_clock,dtn>
其中dtn通常可取以下，当然也可以是自定义Duration类型
std::chrono::hours
std::chrono::minutes
std::chrono::seconds
std::chrono::milliseconds
std::chrono::microseconds
std::chrono::nanoseconds
最常用的的就是
dtn = std::chrono::seconds;
std::chrono::time_point<std::chrono::system_clock,std::chrono::seconds>

example例子

// this_thread::sleep_for example
#include <iostream>       // std::cout
#include <iomanip>        // std::put_time
#include <thread>         // std::this_thread::sleep_until
#include <chrono>         // std::chrono::system_clock
#include <ctime>          // std::time_t, std::tm, std::localtime, 
using std::chrono::time_point;
using std::chrono::system_clock;
using std::system_clock::from_time_t;
using std::tm;
using std::time_t;
using std::mktime;
int main() 
{
    std::tm tm_tp;
    tm_tp.tm_year = 2015 - 1900;
    tm_tp.tm_mon = 7; //0是一月，1是二月，···，7是8月
    tm_tp.tm_mday = 15;
    tm_tp.tm_hour = 19;
    tm_tp.tm_min = 19;
    tm_tp.tm_sec = 19;
    time_t t_tp = mktime(&tm_tp); //得到时间的整数值
    time_point<system_clock> chrono_tp = from_time_t(t_tp);
}

std::tm结构 参考struct tm

chrono::system_clock

　　std::chrono::system_clock表示当前的系统时钟，系统中运行的所有进程使用now()得到的时间是一致的。每一个clock类中都有确定的time_point, duration, Rep, Period类型。

chrono::system_clock::now

static time_point now() noexcept; //获取当前时间time_point

chrono::system_clock::to_time_t

static time_t to_time_t (const time_point& tp) noexcept;//time_point转换成time_t秒

example

#include <iostream>
#include <ctime>
#include <ratio>
#include <chrono>
int main ()
{
  using namespace std::chrono;
  duration<int,std::ratio<60*60*24> > one_day (1);
  system_clock::time_point today = system_clock::now();
  system_clock::time_point tomorrow = today + one_day;
  time_t tt;
  tt = system_clock::to_time_t ( today );
  std::cout << "today is: " << ctime(&tt);
  tt = system_clock::to_time_t ( tomorrow );
  std::cout << "tomorrow will be: " << ctime(&tt);
  return 0;
}

chrono::system_clock::from_time_t

static time_point from_time_t (time_t t) noexcept;

example

#include <iostream>
#include <ctime>
#include <ratio>
#include <chrono>
int main ()
{
  using namespace std::chrono;
  // create tm with 1/1/2000:
  std::tm timeinfo = std::tm();
  timeinfo.tm_year = 100;   // year: 2000
  timeinfo.tm_mon = 0;      // month: january
  timeinfo.tm_mday = 1;     // day: 1st
  std::time_t tt = std::mktime (&timeinfo);
  system_clock::time_point tp = system_clock::from_time_t (tt);
  system_clock::duration d = system_clock::now() - tp;
  // convert to number of days:
  typedef duration<int,std::ratio<60*60*24>> days_type;
  days_type ndays = duration_cast<days_type> (d);
  // display result:
  std::cout << ndays.count() << " days have passed since 1/1/2000";
  std::cout << std::endl;
  return 0;
}

　　chrono最重要就是这几个类，本着够用的原则，其他等需要时再学习