c++11 Chrono时间库的使用小结

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

duration<long, ratio<60>> d1(2);  //2分钟
duration<long, ratio<1>>  d2(30); //30秒
duration<double, ratio<60>> d3 = d1+d2; //2.5分
count << d3.count() << "minutes" << endl;

//X 64 bits表示：有符号整数类型，且位数至少为64位
typedef duration<X 64 bits, nano>  nanoseconds; //纳秒
typedef duration<X 55 bits, micro> microseconds; //微秒
typedef duration<X 45 bits, milli> milliseconds; //毫秒 
typedef duration<X 35 bits>        seconds; //秒 
typedef duration<X 29 bits, ratio<60>>    minutes; //分
typedef duration<X 23 bits, ratio<3600>>  hours; //时

//例
auto t = hours(1) + minutes(2) + seconds(45);
count << seconds(t).count() << endl;

// 均为静态接口
now()  //获取类型为time_point的当前时间点
to_time_t()  //将time_point转换为time_t类型
from_time_t()  //将time_t转换为time_point类型

//获取当前时间
#include <time.h>      // time_t, locaktime, tm
#include <iomanip>     // put_time
system_clock::time_point tpoint = system_clock::now();
time_t tt = system_clock::to_time_t(tpoint);
tm* t = locaktime(&tt);
cout << put_time(t, "%H:%M:%S") << endl;

//计算代码的执行时间
auto start = system_clock::now();
// ... to do something
auto end = system_clock::now();
auto diff = end - start;
cout << duration<double, milli>(diff).count() << "ms" << endl;

time_point();           //通过duration::zero初始化表示关联clock的纪元
time_point(const duration& d); //通过duration初始化表示纪元+d
template<class Duration2>
time_point(const time_point<clock, Duration2>& t); //通过t.time_since_epoch初始化

time_point<steady_clock> tp1;
tp1 += minutes(10);
auto d1 = tp1.time_since_epoch();
duration<double> d2(d1);
cout << d2.count() << "seconds" << endl;

#include <chrono>
#include <thread>


auto begin   = std::chrono::high_resolution_clock::now(); //起始
std::this_thread::sleep_for(std::chrono::milliseconds(800));//运行时长
auto end   = std::chrono::high_resolution_clock::now();//结束

//第一种 使用duration_cast计算
auto duration1 = std::chrono::duration_cast<std::chrono::seconds>(end - begin);
auto duration2 = std::chrono::duration_cast<std::chrono::milliseconds>(end - begin);
auto duration3 = std::chrono::duration_cast<std::chrono::microseconds>(end - begin);
auto duration4 = std::chrono::duration_cast<std::chrono::nanoseconds>(end - begin);

std::cout << duration1.count() << std::endl; //本机测试结果： 0
std::cout << duration2.count() << std::endl; //本机测试结果： 812
std::cout << duration3.count() << std::endl; //本机测试结果： 812698
std::cout << duration4.count() << std::endl; //本机测试结果： 812698500

//第二种 使用durantion
std::chrono::duration<double, std::ratio<1, 1>> elapsed1 = end - begin;
std::chrono::duration<double, std::ratio<1, 1000>> elapsed2 = end - begin;
std::chrono::duration<double, std::ratio<1, 1000000>> elapsed3 = end - begin;
std::chrono::duration<double, std::ratio<1, 1000000000>> elapsed4 = end - begin;

std::cout << elapsed1.count() << std::endl; //本机测试结果： 0.812698
std::cout << elapsed2.count() << std::endl; //本机测试结果： 812.698
std::cout << elapsed3.count() << std::endl; //本机测试结果： 812698
std::cout << std::fixed << std::setprecision(0) << elapsed4.count() << std::endl; //本机测试结果： 812698500

//此处要用system_clock
auto now = std::chrono::system_clock::now();

//下面用到2种转换方式，一种time_point_cast，一种duration_cast

// 获取时间戳，单位为毫秒
auto ms = std::chrono::time_point_cast<std::chrono::milliseconds>(now).time_since_epoch().count();
// 输出毫秒时间戳
std::cout << "Milliseconds timestamp: " << ms << std::endl;

// 获取时间戳，单位为秒
auto sec = std::chrono::duration_cast<std::chrono::seconds>(now.time_since_epoch()).count();
// 输出秒时间戳
std::cout << "Seconds timestamp: " << sec << std::endl;