{"id":4953,"date":"2016-09-20T06:42:10","date_gmt":"2016-09-20T06:42:10","guid":{"rendered":"https:\/\/www.modernescpp.com\/index.php\/time-duration\/"},"modified":"2023-06-26T12:41:49","modified_gmt":"2023-06-26T12:41:49","slug":"time-duration","status":"publish","type":"post","link":"https:\/\/www.modernescpp.com\/index.php\/time-duration\/","title":{"rendered":"Time Duration"},"content":{"rendered":"

Time duration is the difference between two time points. It will be measured in time ticks.<\/p>\n

<\/p>\n

Time duration<\/h2>\n

Time duration is a class template. std::chrono::duration<\/span> consists of the type of the tick Rep<\/span> and the length of a tick Period.<\/span><\/p>\n

<\/p>\n

\n
template<\/span><\r\n    class<\/span> Rep<\/span>,\r\n    class<\/span> Period<\/span> = std::ratio<1>\r\n> class<\/span> duration<\/span>;\r\n<\/pre>\n<\/div>\n
 <\/p>\n
The tick length is by default std::ratio<1><\/span>.  std::ratio<1><\/span> stands for a second and can also be written as std::ratio<1,1><\/span>. Therefore, it’s quite easy. std::ratio<60><\/span> is a minute and std::ratio<1,1000><\/span> a millisecond. When Rep<\/span> is a floating point number, you can use it to hold fractions of time ticks.<\/p>\n
C++11 predefines the most important time durations:<\/p>\n
<\/p>\n
\n
typedef<\/span> duration<signed<\/span> int<\/span>, nano> nanoseconds;\r\ntypedef<\/span> duration<signed<\/span> int<\/span>, micro> microseconds;\r\ntypedef<\/span> duration<signed<\/span> int<\/span>, milli> milliseconds;\r\ntypedef<\/span> duration<signed<\/span> int<\/span>> seconds;\r\ntypedef<\/span> duration<signed<\/span> int<\/span>, ratio< 60>> minutes;\r\ntypedef<\/span> duration<signed<\/span> int<\/span>, ratio<3600>> hours;\r\n<\/pre>\n<\/div>\n
 <\/p>\n
How much time has passed since the UNIX epoch (1.1.1970)? Thanks to type aliases for the different time durations, I can answer the question quite easily. For simplicity reasons, I ignore leap years and assume that a year has 365 days.<\/p>\n
 <\/p>\n
<\/p>\n
\n\n\n\n
\n
 1\r\n 2\r\n 3\r\n 4\r\n 5\r\n 6\r\n 7\r\n 8\r\n 9\r\n10\r\n11\r\n12\r\n13\r\n14\r\n15\r\n16\r\n17\r\n18\r\n19\r\n20\r\n21\r\n22\r\n23\r\n24\r\n25\r\n26\r\n27\r\n28\r\n29\r\n30\r\n31\r\n32\r\n33\r\n34\r\n35\r\n36\r\n37\r\n38\r\n39\r\n40\r\n41\r\n42\r\n43\r\n44\r\n45\r\n46<\/pre>\n<\/td>\n
\n
\/\/ timeSinceEpoch.cpp<\/span>\r\n\r\n#include <chrono><\/span>\r\n#include <iostream><\/span>\r\n\r\nint<\/span> main(){\r\n\r\n  std::cout << std::fixed << std::endl;\r\n  \r\n  std::cout << \"Time since 1.1.1970:\\n\"<\/span> << std::endl;\r\n\r\n  auto<\/span> timeNow= std::chrono::system_clock::now();\r\n  auto<\/span> duration= timeNow.time_since_epoch();\r\n  std::cout << duration.count() << \" nanoseconds \"<\/span> << std::endl;\r\n\r\n  typedef<\/span> std::chrono::duration<long<\/span> double<\/span>,std::ratio<1,1000000>> MyMicroSecondTick;\r\n  MyMicroSecondTick micro(duration);\r\n  std::cout << micro.count() << \" microseconds\"<\/span> << std::endl;\r\n  \r\n  typedef<\/span> std::chrono::duration<long<\/span> double<\/span>,std::ratio<1,1000>> MyMilliSecondTick;\r\n  MyMilliSecondTick milli(duration);\r\n  std::cout << milli.count() << \" milliseconds\"<\/span> << std::endl;\r\n  \r\n  typedef<\/span> std::chrono::duration<long<\/span> double<\/span>> MySecondTick;\r\n  MySecondTick sec(duration);\r\n  std::cout << sec.count() << \" seconds \"<\/span> << std::endl;\r\n  \r\n  typedef<\/span> std::chrono::duration<double<\/span>, std::ratio<60>> MyMinuteTick;\r\n  MyMinuteTick myMinute(duration);\r\n  std::cout << myMinute.count() << \" minutes\"<\/span> << std::endl;\r\n\r\n  typedef<\/span> std::chrono::duration<double<\/span>, std::ratio<60*60>> MyHourTick;\r\n  MyHourTick myHour(duration);\r\n  std::cout << myHour.count() << \" hours\"<\/span> << std::endl;\r\n  \r\n  typedef<\/span> std::chrono::duration<double<\/span>, std::ratio<60*60*24*365>> MyYearTick;\r\n  MyYearTick myYear(duration);\r\n  std::cout << myYear.count() << \" years\"<\/span> << std::endl;\r\n\r\n  typedef<\/span> std::chrono::duration<double<\/span>, std::ratio<60*45>> MyLessonTick;\r\n  MyLessonTick myLesson(duration);\r\n  std::cout << myLesson.count() << \" lessons\"<\/span> << std::endl;\r\n\r\n  std::cout << std::endl;\r\n\r\n}\r\n<\/pre>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n
 <\/p>\n
In addition to the typical time duration’s microsecond (line 16), millisecond (line 20), second (line 24), minute (line 28), hour (line 32), and year (line 36), I define the German school hour (45 min) in line 45.<\/p>\n
 \"timeSinceEpoch\"<\/p>\n
It’s quite convenient to calculate with time durations.<\/p>\n<\/p>\n
Calculations with time durations<\/h2>\n
The time durations support basic mathematics. In the case of multiplication or division, you can multiply or divide a time duration by a number. Of course, you can compare time durations. I explicitly want to emphasize that all these calculations and comparisons respect the units of the time durations.<\/p>\n
It gets even better with C++14 because C++14 has a bunch of predefined time literals.<\/p>\n
\"timeLiteralsEng\"<\/p>\n
How much time does my 16 year old son need for his typical school day? I will answer the question in the example and show the result in different time durations.<\/p>\n
<\/p>\n
\n\n\n\n
\n
 1\r\n 2\r\n 3\r\n 4\r\n 5\r\n 6\r\n 7\r\n 8\r\n 9\r\n10\r\n11\r\n12\r\n13\r\n14\r\n15\r\n16\r\n17\r\n18\r\n19\r\n20\r\n21\r\n22\r\n23\r\n24\r\n25\r\n26\r\n27\r\n28\r\n29\r\n30\r\n31\r\n32\r\n33\r\n34<\/pre>\n<\/td>\n
\n
\/\/ schoolDay.cpp<\/span>\r\n\r\n#include <iostream><\/span>\r\n#include <chrono><\/span>\r\n\r\nusing<\/span> namespace<\/span> std::literals::chrono_literals;\r\n\r\nint<\/span> main(){\r\n\r\n  std::cout << std::endl;\r\n\r\n  constexpr auto<\/span> schoolHour= 45min;\r\n\r\n  constexpr auto<\/span> shortBreak= 300s;\r\n  constexpr auto<\/span> longBreak= 0.25h;\r\n\r\n  constexpr auto<\/span> schoolWay= 15min;\r\n  constexpr auto<\/span> homework= 2h;\r\n\r\n  constexpr auto<\/span> schoolDayInSeconds= 2*schoolWay + 6 * schoolHour + 4 * shortBreak + longBreak + homework;\r\n\r\n  std::cout << \"School day in seconds: \"<\/span> << schoolDayInSeconds.count() << std::endl;\r\n\r\n  std::chrono::duration<double<\/span>,std::ratio<3600>> schoolDayInHours = schoolDayInSeconds;\r\n  std::chrono::duration<double<\/span>,std::ratio<60>> schoolDayInMinutes = schoolDayInSeconds;\r\n  std::chrono::duration<double<\/span>,std::ratio<1,1000>> schoolDayInMilliseconds= schoolDayInSeconds;\r\n\r\n  std::cout << \"School day in hours: \"<\/span> << schoolDayInHours.count() << std::endl;\r\n  std::cout << \"School day in minutes: \"<\/span> << schoolDayInMinutes.count() << std::endl;\r\n  std::cout << \"School day in milliseconds: \"<\/span> << schoolDayInMilliseconds.count() << std::endl;\r\n\r\n  std::cout << std::endl;\r\n\r\n}\r\n<\/pre>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n
 <\/p>\n
The time literals are constant expressions<\/a>; therefore, they can be evaluated at compile time. I have time durations for a German school hour (line 12), for a short break (line 14), for a long break (line 15), for his way to the school (line 17), and his homework (line 18). The result of the calculation schoolDaysInSeconds<\/span> (line 20) is available at compile time.<\/p>\n
\"schoolDay\"<\/p>\n
Impressed? I’m not. His daily duty is only about 7 1\/2 hours.<\/p>\n
What’s next?<\/h2>\n
The used clock gives the accuracy of the time tick. In C++, we have the clocks std::chrono::system_clock,<\/span> std::chrono::steady_clock,<\/span> and std::chrono::high_resolution_clock. <\/span>The three clocks will be the topic of my next post<\/a>.<\/p>\n
 <\/p>\n
 <\/p>\n
 <\/p>\n
 <\/p>\n
 <\/p>\n","protected":false},"excerpt":{"rendered":"
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