cartographer時間相關知識點
1 #include <chrono> 2 #include <ostream> 3 #include <ratio> 4 5 #include "cartographer/common/port.h" 6 7 namespace cartographer { 8 namespace common { 9 10 constexpr int64 kUtsEpochOffsetFromUnixEpochInSeconds = 11 (719162ll * 24ll * 60ll * 60ll);//719162ll/365=1970.3 12 13struct UniversalTimeScaleClock { 14 using rep = int64; 15 using period = std::ratio<1, 10000000>;//單位10ns 16 using duration = std::chrono::duration<rep, period>; 17 using time_point = std::chrono::time_point<UniversalTimeScaleClock>; 18 static constexpr bool is_steady = true; 19 };20 21 // Represents Universal Time Scale durations and timestamps which are 64-bit 22 // integers representing the 100 nanosecond ticks since the Epoch which is 23 // January 1, 1 at the start of day in UTC. 24 using Duration = UniversalTimeScaleClock::duration; 25 using Time = UniversalTimeScaleClock::time_point;26 27 // Convenience functions to create common::Durations. 28 Duration FromSeconds(double seconds); 29 Duration FromMilliseconds(int64 milliseconds); 30 31 // Returns the given duration in seconds. 32 double ToSeconds(Duration duration); 33 double ToSeconds(std::chrono::steady_clock::duration duration); 34 35 // Creates a time from a Universal Time Scale. 36 Time FromUniversal(int64 ticks); 37 38 // Outputs the Universal Time Scale timestamp for a given Time. 39 int64 ToUniversal(Time time); 40 41 // For logging and unit tests, outputs the timestamp integer. 42 std::ostream& operator<<(std::ostream& os, Time time); 43 44 // CPU time consumed by the thread so far, in seconds. 45 double GetThreadCpuTimeSeconds(); 46 47 } // namespace common 48 } // namespace cartographer
下面對上面的程式碼進行解釋:
1、第一行的標頭檔案#include <chrono>
在C++11中,<chrono>是標準模板庫中與時間有關的標頭檔案。該標頭檔案中所有函式與類模板均定義在std::chrono名稱空間中。
std::chrono::duration:記錄時間長度,表示一段時間,如1分鐘、2小時、10毫秒等。表示為類模板duration的物件,用一個count representation與一個period precision表示。例如,10毫秒的10為count representation,毫秒為period precision。
第一個模板引數為表示時間計數的資料型別。成員函式count返回該計數。第二個模板引數表示計數的一個週期,一般是std::ratio型別,表示一個週期(即一個時間滴答tick)是秒鐘的倍數或分數,在編譯時應為一個有理常量。
std::chrono::time_point:記錄時間點的,表示一個具體的時間。例如某人的生日、今天的日出時間等。表示為類模板time_point的物件。用相對於一個固定時間點epoch的duration來表示。
std::chrono::clocks:時間點相對於真實物理時間的框架。至少提供了3個clock:
1)system_clock:當前系統範圍(即對各程序都一致)的一個實時的日曆時鐘(Wallclock)。
2)steady_clock:當前系統實現的一個維定時鐘,該時鐘的每個時間滴答單位是均勻的(即長度相等)。
3)high_resolution_clock:當前系統實現的一個高解析度時鐘。
#include <chrono> #include <iostream> #include <ratio> #include <ctime> #include <iomanip> /////////////////////////////////////////////////////////////// // reference: http://www.cplusplus.com/reference/chrono/duration/ int test_chrono_duration() { { // duration::duration: Constructs a duration object // chrono::duration_cast: Converts the value of dtn into some other duration type, // taking into account differences in their periods typedef std::chrono::duration<int> seconds_type; //template<typename _Rep, typename _Period> struct duration,前面是型別,後面是單位 typedef std::chrono::duration<int, std::milli> milliseconds_type;//typedef ratio<1, 1000> milli; typedef std::chrono::duration<int, std::ratio<60 * 60>> hours_type; //template<intmax_t _Num, intmax_t _Den = 1>,分母預設值為1 hours_type h_oneday(24); // 24h seconds_type s_oneday(60 * 60 * 24); // 86400s milliseconds_type ms_oneday(s_oneday); // 86400000ms seconds_type s_onehour(60 * 60); // 3600s //hours_type h_onehour (s_onehour); // NOT VALID (type truncates), use: hours_type h_onehour(std::chrono::duration_cast<hours_type>(s_onehour)); milliseconds_type ms_onehour(s_onehour); // 3600000ms (ok, no type truncation) std::cout << ms_onehour.count() << "ms in 1h" << std::endl; } { // duration operators: +、-、*、/、>、<、!=、and so on std::chrono::duration<int> foo; //預設單位都是秒 std::chrono::duration<int> bar(10); // counts: foo bar // --- --- foo = bar; // 10 10 foo = foo + bar; // 20 10 ++foo; // 21 10 --bar; // 21 9 foo *= 2; // 42 9 foo /= 3; // 14 9 //bar += (foo % bar); // 14 14 std::cout << std::boolalpha; std::cout << "foo==bar: " << (foo == bar) << std::endl; std::cout << "foo: " << foo.count() << std::endl; std::cout << "bar: " << bar.count() << std::endl; } { // duration::count: Returns the internal count (i.e., the representation value) of the duration object. using namespace std::chrono; // std::chrono::milliseconds is an instatiation of std::chrono::duration: milliseconds foo(1000); // 1 second foo *= 60; std::cout << "duration (in periods): "; std::cout << foo.count() << " milliseconds.\n"; std::cout << "duration (in seconds): "; std::cout << foo.count() * milliseconds::period::num / milliseconds::period::den; std::cout << " seconds.\n"; } { // duration::max: Returns the maximum value of duration // duration::min: Returns the minimum value of duration std::cout << "system_clock durations can represent:\n"; std::cout << "min: " << std::chrono::system_clock::duration::min().count() << "\n"; std::cout << "max: " << std::chrono::system_clock::duration::max().count() << "\n"; } { // duration::zero: Returns a duration value of zero using std::chrono::steady_clock; steady_clock::time_point t1 = steady_clock::now(); std::cout << "Printing out something...\n"; steady_clock::time_point t2 = steady_clock::now(); steady_clock::duration d = t2 - t1; if (d == steady_clock::duration::zero()) std::cout << "The internal clock did not tick.\n"; else std::cout << "The internal clock advanced " << d.count() << " periods.\n"; } { // chrono::time_point_cast: Converts the value of tp into a time_point type with a different duration internal object, // taking into account differences in their durations's periods. using namespace std::chrono; typedef duration<int, std::ratio<60 * 60 * 24>> days_type; time_point<system_clock, days_type> today = time_point_cast<days_type>(system_clock::now()); std::cout << today.time_since_epoch().count() << " days since epoch" << std::endl; } return 0; } ////////////////////////////////////////////////////////////////// // reference: http://www.cplusplus.com/reference/chrono/high_resolution_clock/ int test_chrono_high_resolution_clock() { // high_resolution_clock::now: Returns the current time_point in the frame of the high_resolution_clock using namespace std::chrono; high_resolution_clock::time_point t1 = high_resolution_clock::now(); std::cout << "printing out 1000 stars...\n"; for (int i = 0; i<1000; ++i) std::cout << "*"; std::cout << std::endl; high_resolution_clock::time_point t2 = high_resolution_clock::now(); duration<double> time_span = duration_cast<duration<double>>(t2 - t1); std::cout << "It took me " << time_span.count() << " seconds."; std::cout << std::endl; return 0; } /////////////////////////////////////////////////////////////////////// // reference: http://www.cplusplus.com/reference/chrono/steady_clock/ int test_chrono_steady_clock() { // steady_clock is specifically designed to calculate time intervals. // steady_clock::now: Returns the current time_point in the frame of the steady_clock. using namespace std::chrono; steady_clock::time_point t1 = steady_clock::now(); std::cout << "printing out 1000 stars...\n"; for (int i = 0; i<1000; ++i) std::cout << "*"; std::cout << std::endl; steady_clock::time_point t2 = steady_clock::now(); duration<double> time_span = duration_cast<duration<double>>(t2 - t1); std::cout << "It took me " << time_span.count() << " seconds."; std::cout << std::endl; return 0; } ////////////////////////////////////////////////////////////// // reference: http://www.cplusplus.com/reference/chrono/system_clock/ int test_chrono_system_clock() { // system_clock is a system-wide realtime clock. { // system_clock::from_time_t: Converts t into its equivalent of member type time_point. 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; } { // system_clock::now: Returns the current time_point in the frame of the system_clock 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); } { // system_clock::to_time_t: Converts tp into its equivalent of type time_t. 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; } ////////////////////////////////////////////////////// // reference: http://www.cplusplus.com/reference/chrono/time_point/ int test_chrono_time_point() { { // time_point operators: +、-、==、!= using namespace std::chrono; system_clock::time_point tp, tp2; // epoch value system_clock::duration dtn(duration<int>(1)); // 1 second // tp tp2 dtn // --- --- --- tp += dtn; // e+1s e 1s tp2 -= dtn; // e+1s e-1s 1s tp2 = tp + dtn; // e+1s e+2s 1s tp = dtn + tp2; // e+3s e+2s 1s tp2 = tp2 - dtn; // e+3s e+1s 1s dtn = tp - tp2; // e+3s e+1s 2s std::cout << std::boolalpha; std::cout << "tp == tp2: " << (tp == tp2) << std::endl; std::cout << "tp > tp2: " << (tp>tp2) << std::endl; std::cout << "dtn: " << dtn.count() << std::endl; } { // time_point::time_point: Constructs a time_point object using namespace std::chrono; system_clock::time_point tp_epoch; // epoch value time_point <system_clock, duration<int>> tp_seconds(duration<int>(1)); system_clock::time_point tp(tp_seconds); std::cout << "1 second since system_clock epoch = "; std::cout << tp.time_since_epoch().count(); std::cout << " system_clock periods." << std::endl; // display time_point: std::time_t tt = system_clock::to_time_t(tp); std::cout << "time_point tp is: " << ctime(&tt); } { // time_point::time_since_epoch: Returns a duration object with the time span value between the epoch and the time point using namespace std::chrono; system_clock::time_point tp = system_clock::now(); system_clock::duration dtn = tp.time_since_epoch(); std::cout << "current time since epoch, expressed in:" << std::endl; std::cout << "periods: " << dtn.count() << std::endl; std::cout << "seconds: " << dtn.count() * system_clock::period::num / system_clock::period::den; std::cout << std::endl; } return 0; } /////////////////////////////////////////////////////////////////// // reference: https://zh.wikibooks.org/wiki/C%2B%2B/STL/Chrono static long fibonacci(unsigned n) { if (n < 2) return n; return fibonacci(n - 1) + fibonacci(n - 2); } int test_chrono_1() { { // std::chrono::time_point std::chrono::system_clock::time_point now = std::chrono::system_clock::now(); std::time_t now_c = std::chrono::system_clock::to_time_t(now - std::chrono::hours(24)); std::cout << "24 hours ago, the time was " << now_c << '\n'; std::chrono::steady_clock::time_point start = std::chrono::steady_clock::now(); std::cout << "Hello World\n"; std::chrono::steady_clock::time_point end = std::chrono::steady_clock::now(); std::cout << "Printing took " << std::chrono::duration_cast<std::chrono::microseconds>(end - start).count() << "us.\n"; } { // std::chrono::duration using shakes = std::chrono::duration<int, std::ratio<1, 100000000>>; using jiffies = std::chrono::duration<int, std::centi>; using microfortnights = std::chrono::duration<float, std::ratio<12096, 10000>>; using nanocenturies = std::chrono::duration<float, std::ratio<3155, 1000>>; std::chrono::seconds sec(1); std::cout << "1 second is:\n"; std::cout << std::chrono::duration_cast<shakes>(sec).count() << " shakes\n"; std::cout << std::chrono::duration_cast<jiffies>(sec).count() << " jiffies\n"; std::cout << microfortnights(sec).count() << " microfortnights\n"; std::cout << nanocenturies(sec).count() << " nanocenturies\n"; } { // std::chrono::time_point<std::chrono::system_clock> start, end; start = std::chrono::system_clock::now(); std::cout << "f(42) = " << fibonacci(42) << '\n'; end = std::chrono::system_clock::now(); std::chrono::duration<double> elapsed_seconds = end - start; std::time_t end_time = std::chrono::system_clock::to_time_t(end); std::cout << "finished computation at " << std::ctime(&end_time) << "elapsed time: " << elapsed_seconds.count() << "s\n"; } return 0; } int main(int argc, char** argv) { test_chrono_duration(); return 0; }View Code
看一下時間點,參考其他部落格,再次寫一下chrono相關的知識
chrono是一個time library, 源於boost,現在已經是C++標準。話說今年似乎又要出新標準了,好期待啊!
要使用chrono庫,需要#include<chrono>,其所有實現均在std::chrono namespace下。注意標準庫裡面的每個名稱空間代表了一個獨立的概念。所以下文中的概念均以名稱空間的名字表示!chrono是一個模版庫,使用簡單,功能強大,只需要理解三個概念:duration、time_point、clock
1)、
Durations std::chrono::duration 表示一段時間,比如兩個小時,12.88秒,半個時辰,一炷香的時間等等,只要能換算成秒即可。template <class Rep, class Period = ratio<1> > class duration;其中 Rep表示一種數值型別,用來表示Period的數量,比如int float double Period是ratio型別,用來表示【用秒錶示的時間單位】比如second milisecond 常用的duration<Rep,Period>已經定義好了,在std::chrono::duration下: ratio<3600, 1> hours ratio<60, 1> minutes ratio<1, 1> seconds ratio<1, 1000> microseconds ratio<1, 1000000> microseconds ratio<1, 1000000000> nanosecons 這裡需要說明一下ratio這個類模版的原型:
template <intmax_t N, intmax_t D = 1> class ratio;N代表分子,D代表分母,所以ratio表示一個分數值。 注意,我們自己可以定義Period,比如ratio<1, -2>表示單位時間是-0.5秒。
由於各種duration表示不同,chrono庫提供了duration_cast型別轉換函式。
1 template <class ToDuration, class Rep, class Period> 2 constexpr ToDuration duration_cast (const duration<Rep,Period>& dtn);
典型用法:
// duration constructor #include <iostream> #include <ratio> #include <chrono> int main () { typedef std::chrono::duration<int> seconds_type; typedef std::chrono::duration<int,std::milli> milliseconds_type; typedef std::chrono::duration<int,std::ratio<60*60>> hours_type; hours_type h_oneday (24); // 24h seconds_type s_oneday (60*60*24); // 86400s milliseconds_type ms_oneday (s_oneday); // 86400000ms seconds_type s_onehour (60*60); // 3600s //hours_type h_onehour (s_onehour); // NOT VALID (type truncates), use: hours_type h_onehour (std::chrono::duration_cast<hours_type>(s_onehour)); milliseconds_type ms_onehour (s_onehour); // 3600000ms (ok, no type truncation) std::cout << ms_onehour.count() << "ms in 1h" << std::endl; return 0; } duration還有一個成員函式count()返回Rep型別的Period數量,看程式碼: // duration::count #include <iostream> // std::cout #include <chrono> // std::chrono::seconds, std::chrono::milliseconds // std::chrono::duration_cast int main () { using namespace std::chrono; // std::chrono::milliseconds is an instatiation of std::chrono::duration: milliseconds foo (1000); // 1 second foo*=60; std::cout << "duration (in periods): "; std::cout << foo.count() << " milliseconds.\n"; std::cout << "duration (in seconds): "; std::cout << foo.count() * milliseconds::period::num / milliseconds::period::den; std::cout << " seconds.\n"; return 0; }View Code
2)Time points
std::chrono::time_point表示一個具體時間,如上個世紀80年代、你的生日、今天下午、火車出發時間等,只要它能用計算機時鐘表示。鑑於我們使用時間的情景不同,這個time point具體到什麼程度,由選用的單位決定。一個time point必須有一個clock計時。
template<class Clock, class Duration = typename Clock::duration> class time_point;
下面是構造使用time_point的例子
// time_point constructors #include <iostream> #include <chrono> #include <ctime> int main () { using namespace std::chrono; system_clock::time_point tp_epoch; // epoch value time_point <system_clock,duration<int>> tp_seconds (duration<int>(1)); system_clock::time_point tp (tp_seconds); std::cout << "1 second since system_clock epoch = "; std::cout << tp.time_since_epoch().count(); std::cout << " system_clock periods." << std::endl; // display time_point: std::time_t tt = system_clock::to_time_t(tp); std::cout << "time_point tp is: " << ctime(&tt); return 0; }View Code time_point有一個函式time_from_eproch()用來獲得1970年1月1日到time_point時間經過的duration。 舉個例子,如果timepoint以天為單位,函式返回的duration就以天為單位。 由於各種time_point表示方式不同,chrono也提供了相應的轉換函式 time_point_cast。
1 template <class ToDuration, class Clock, class Duration> 2 time_point<Clock,ToDuration> time_point_cast (const time_point<Clock,Duration>& tp);
/ time_point_cast #include <iostream> #include <ratio> #include <chrono> int main () { using namespace std::chrono; typedef duration<int,std::ratio<60*60*24>> days_type; time_point<system_clock,days_type> today = time_point_cast<days_type>(system_clock::now()); std::cout << today.time_since_epoch().count() << " days since epoch" << std::endl; return 0; }View Code
3)clocks
std::chrono::system_clock 它表示當前的系統時鐘,系統中執行的所有程序使用now()得到的時間是一致的。 每一個clock類中都有確定的time_point, duration, Rep, Period型別。 操作有: now() 當前時間time_point to_time_t() time_point轉換成time_t秒 from_time_t() 從time_t轉換成time_point 典型的應用是計算時間日期:// system_clock example #include <iostream> #include <ctime> #include <ratio> #include <chrono> int main () { using std::chrono::system_clock; 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; std::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; }View Code
std::chrono::steady_clock 為了表示穩定的時間間隔,後一次呼叫now()得到的時間總是比前一次的值大(這句話的意思其實是,如果中途修改了系統時間,也不影響now()的結果),每次tick都保證過了穩定的時間間隔。
操作有: now() 獲取當前時鐘 典型的應用是給演算法計時:// steady_clock example #include <iostream> #include <ctime> #include <ratio> #include <chrono> int main () { using namespace std::chrono; steady_clock::time_point t1 = steady_clock::now(); std::cout << "printing out 1000 stars...\n"; for (int i=0; i<1000; ++i) std::cout << "*"; std::cout << std::endl; steady_clock::time_point t2 = steady_clock::now(); duration<double> time_span = duration_cast<duration<double>>(t2 - t1); std::cout << "It took me " << time_span.count() << " seconds."; std::cout << std::endl; return 0; }View Code
最後一個時鐘,std::chrono::high_resolution_clock 顧名思義,這是系統可用的最高精度的時鐘。實際上high_resolution_clock只不過是system_clock或者steady_clock的typedef。
2、第三行#include <ratio>
其是在c++11中引入的,模板類std::ratio以及相關的模板類(如std::ratio_add)提供編譯時有理數算術支援。
此模板的每個例項化都準確表示任意有限有理數。他們都是用來表示比例關係的模板類。
宣告
template<intmax_t N, intmax_t D = 1> class ratio;
其中N表示分子,D表示分母;intmax_t表示最大的有符號整數型別,N和D的絕對值都應該在intmax_t可表示的範圍內,D不能為0.
std::ratio類一般不通過它的物件來表示,而是這個型別本身來表示的,但也可以通過它的物件來表示。std::ratio有兩個成員常量:num表示的是分子,den表示的是分母。這裡的num和den已經經過化簡,因此輸出值可能和定義時傳入的不同,如typedef std::ratio<100, 10> ratio1, 輸出值ratio1::num為10,ratio1::den為1,求其最大公約數。
在include<ratio>中,除std::ratio外,還有編譯時有理數算術:std::ratio_add、std::ratio_subtract、std::ratio_multiply、std::ratio_divide,它們和std::ratio一樣,也都有兩個成員常量:num和den。編譯時有理數比較:std::ratio_equal、std::ratio_not_equal、std::ratio_less、std::ratio_less_equal、std::ratio_greater、std::ratio_greater_equal,它們都有value成員常量。它們的計算公式如下:
template <typename R1, typename R2> using ratio_add = ratio < R1::num*R2::den+R2::num*R1::den, R1::den*R2::den > template <typename R1, typename R2> using ratio_subtract = std::ratio < R1::num*R2::den-R2::num*R1::den, R1::den*R2::den > template <typename R1, typename R2> using ratio_multiply = std::ratio < R1::num * R2::num, R1::den * R2::den >; template <typename R1, typename R2> using ratio_divide = ratio < R1::num * R2::den, R2::num * R1::den >; template <class R1, class R2> struct ratio_equal : integral_constant<bool, R1::num==R2::num && R1::den==R2::den> {} template <class R1, class R2> struct ratio_less : integral_constant < bool, R1::num*R2::den < R2::num*R1::den > {}; template <class R1, class R2> struct ratio_greater : integral_constant < bool, ratio_less<R2,R1>::value > {}; template <class R1, class R2> struct ratio_greater_equal : integral_constant < bool, !ratio_less<R1,R2>::value > {}; template <class R1, class R2> struct ratio_less_equal : integral_constant < bool, !ratio_less<R2,R1>::value > {} template <class R1, class R2> struct ratio_equal : integral_constant < bool, !ratio_equal<R1,R2>::value > {};View Code
#include "ratio.hpp" #include <iostream> #include <ratio> // // reference: http://www.cplusplus.com/reference/ratio/ int test_ratio_1() { typedef std::ratio<1, 3> one_third; typedef std::ratio<2, 4> two_fourths; typedef std::ratio<2, 3> two_thirds; typedef std::ratio<1, 2> one_half; std::cout << "one_third= " << one_third::num << "/" << one_third::den << std::endl; std::cout << "two_fourths= " << two_fourths::num << "/" << two_fourths::den << std::endl; // Note: 1/2 std::cout << "two_thirds= " << two_thirds::num << "/" << two_thirds::den << std::endl; std::cout << "one_half= " << one_half::num << "/" << one_half::den << std::endl; std::cout << std::endl; { // std::ratio typedef std::ratio_add<one_third, two_fourths> sum; std::cout << "sum= " << sum::num << "/" << sum::den; std::cout << " (which is: " << (double(sum::num) / sum::den) << ")" << std::endl; std::cout << "1 kilogram has " << (std::kilo::num / std::kilo::den) << " grams"; std::cout << std::endl; } { // std::ratio_add typedef std::ratio_add<one_half, two_thirds> sum; std::cout << "sum = " << sum::num << "/" << sum::den; std::cout << " (which is: " << (double(sum::num) / sum::den) << ")" << std::endl; } { // std::ratio_subtract typedef std::ratio_subtract<two_thirds, one_half> diff; std::cout << "diff = " << diff::num << "/" << diff::den; std::cout << " (which is: " << (double(diff::num) / diff::den) << ")" << std::endl; } { // std::ratio_multiply typedef std::ratio_multiply<one_half, one_third> result; std::cout << "result = " << result::num << "/" << result::den; std::cout << " (which is: " << (double(result::num) / result::den) << ")" << std::endl; } { // std::ratio_divide typedef std::ratio_divide<one_half, one_third> result; std::cout << "result = " << result::num << "/" << result::den; std::cout << " (which is: " << (double(result::num) / result::den) << ")" << std::endl; std::cout << std::endl; } { // std::ratio_equal std::cout << "1/2 == 2/4 ? " << std::boolalpha; std::cout << std::ratio_equal<one_half, two_fourths>::value << std::endl; } { // std::ratio_greater std::cout << "1/3 > 1/2 ? " << std::boolalpha; std::cout << std::ratio_greater<one_third, one_half>::value << std::endl; } { // std::ratio_greater_equal std::cout << "1/3 >= 1/2 ? " << std::boolalpha; std::cout << std::ratio_greater_equal<one_third, one_half>::value << std::endl; } { // std::ratio_less std::cout << "1/3 < 1/2 ? " << std::boolalpha; std::cout << std::ratio_less<one_third, one_half>::value << std::endl; } { // std::ratio_less_equal std::cout << "1/3 <= 1/2 ? " << std::boolalpha; std::cout << std::ratio_less_equal<one_third, one_half>::value << std::endl; } { // std::ratio_not_equal std::cout << "1/2 != 2/4 ? " << std::boolalpha; std::cout << std::ratio_not_equal<one_half, two_fourths>::value << std::endl; } std::cout << std::endl; return 0; } / // reference: https://stackoverflow.com/questions/25005205/why-can-i-have-a-ratio-object-in-c int test_ratio_2() { // If you don't use a typedef you're creating an instance of std::ratio<1, 3> named one_third, // which is not suitable for passing as a type argument.In that case you'll need to use decltype // to get to the appropriate type that can be passed to ratio_add std::ratio<1, 3> one_third; std::ratio<2, 4> two_fourths; std::ratio_add<decltype(one_third), decltype(two_fourths)> sum; std::cout << decltype(sum)::den << std::endl; return 0; }View Code
std::ratio<num, den> 定義分式
std::ratio<60, 1> minutes;//<分子,分母>一分鐘60秒 std::ratio<60 * 60> hource;//1小時3600秒 std::ratio<1, 1000> milliseconds; //1ms是1/1000秒
chrono名稱空間定義好的時間單位
typedef duration <Rep, ratio<3600,1>> hours; typedef duration <Rep, ratio<60,1>> minutes; typedef duration <Rep, ratio<1,1>> seconds; typedef duration <Rep, ratio<1,1000>> milliseconds; typedef duration <Rep, ratio<1,1000000>> microseconds; typedef duration <Rep, ratio<1,1000000000>> nanoseconds;
舉例
chrono::minutes mintu{2};//2分鐘 chrono::seconds sec{3};//3秒鐘 chrono::milliseconds mills{500};//500毫秒 auto dul = sec - mills;//兩者差值,單位預設轉到更小的 2500ms dul.count(); //值為2500 std::this_thread::sleep_for(std::chrono::milliseconds(100)); //當前執行緒休眠100毫秒
time.cc
#include "cartographer/common/time.h" #include <time.h> #include <cerrno> #include <cstring> #include <string> #include "glog/logging.h" namespace cartographer { namespace common { Duration FromSeconds(const double seconds) { return std::chrono::duration_cast<Duration>( std::chrono::duration<double>(seconds)); } double ToSeconds(const Duration duration) { return std::chrono::duration_cast<std::chrono::duration<double>>(duration) .count(); } double ToSeconds(const std::chrono::steady_clock::duration duration) { return std::chrono::duration_cast<std::chrono::duration<double>>(duration) .count(); } Time FromUniversal(const int64 ticks) { //using duration = std::chrono::duration<rep, period>; // using time_point = std::chrono::time_point<UniversalTimeScaleClock>; printf("ticks is %ld ", ticks);//add by gary printf("Duration'count is %lf ",Duration(ticks).count()); printf("Time is %lf\n",Time(Duration(ticks)).time_since_epoch().count()); return Time(Duration(ticks)); } int64 ToUniversal(const Time time) { return time.time_since_epoch().count(); } std::ostream& operator<<(std::ostream& os, const Time time) { os << std::to_string(ToUniversal(time)); return os; } common::Duration FromMilliseconds(const int64 milliseconds) { return std::chrono::duration_cast<Duration>( std::chrono::milliseconds(milliseconds)); } double GetThreadCpuTimeSeconds() { #ifndef WIN32 struct timespec thread_cpu_time; CHECK(clock_gettime(CLOCK_THREAD_CPUTIME_ID, &thread_cpu_time) == 0) << std::strerror(errno); return thread_cpu_time.tv_sec + 1e-9 * thread_cpu_time.tv_nsec; #else return 0.; #endif } } // namespace common } // namespace cartographer