[Most needed time and date methods] – [Measuring execution time] – [General infos] –
Most needed time and date methods
#include <chrono>
#include <iostream>
using namespace std::chrono;
void TestDateAndTime()
{
std::cout << "Simply requesting (UTC) time:" << "\n";
const auto utcTime = system_clock::now(); // std::chrono::time_point
std::cout << "nowTime : " << utcTime << "\n";
std::cout << "\nUsing formaters, current time zone and local time:" << "\n";
const auto time = current_zone()->to_local(utcTime); // std::chrono::time_point
std::cout << "Time zone : " << current_zone()->name() << "\n";
std::cout << "Date : " << std::format("{:%d.%m.%y}", time)
<< " or " << std::format("{:%d.%m.%Y}", time) << "\n";
std::cout << "Time : " << std::format("{:%H:%M}", time)
<< " or " << std::format("{:%X}", time) << "\n";
std::cout << "TimeWithExactSec : " << std::format("{:%H:%M:%S}", time) << "\n";
std::cout << "Calendar week : " << std::format("{:%W}", time) << "\n";
std::cout << "DayOfYear : " << std::format("{:%j}", time) << "\n";
std::cout << "Weekday : " << std::format("{:%a}", time)
<< " or " << std::format("{:%A}", time) << "\n";
std::cout << "\nCalculations with time and date:" << "\n";
const auto currentDate = year_month_day{ floor<days>(time) };
const int thisYear = int(currentDate.year());
const unsigned int thisMonth = static_cast<unsigned>(currentDate.month());
// Calculate future time point
const auto futureTimePointSomeDeltaLater = time + 20h + 10min + 5s;
// Check for leap year
const auto leapYearCheck{ year(currentDate.year())/2/29};
const bool isLeapYear = leapYearCheck.ok(); // checks validity of leap day
// Days since 1.1., days left until 31.12.
const int dayOfYear = (floor<days>(utcTime)
- sys_days(year(thisYear - 1) / 12 / 31)).count();
const int daysLeftInYear = (sys_days(year(thisYear) / 12 / 31)
- floor<days>(utcTime)).count();
std::cout << "FutureTimePoint : " << std::format("{:%d.%m.%Y %X}",
futureTimePointSomeDeltaLater) << "\n";
std::cout << "LeapYear : " << thisYear << (isLeapYear
? " is a leapYear" : " is no leapYear") << "\n";
std::cout << "Last day of month : " << year_month_day{ year(thisYear)
/ month(thisMonth) / last } << "\n";
std::cout << "Second Monday of month : " << year_month_day{ year(thisYear)
/ month(thisMonth) / Monday[2]} << "\n";
std::cout << "Last Friday of month : " << year_month_day{ year(thisYear)
/ month(thisMonth) / Friday[last] } << "\n";
std::cout << "DayOfYear : " << dayOfYear << "\n";
std::cout << "DaysLeftInYear : " << daysLeftInYear << "\n";
std::cout << "\nCalculations with Mozart:" << "\n";
constexpr auto mozartBirthday{ day(27) / month(1) / year(1756) };
constexpr auto mozartDeathday{ day(5) / month(12) / year(1791) };
const auto daysLived = floor<days>(sys_days(mozartDeathday) - sys_days(mozartBirthday));
const int daysLivedInt = daysLived.count(); // daysLived has type std::chrono::duration
const int yearsLived = floor<years>(daysLived).count();
const int yearsSinceBirth = floor<years>((sys_days(year_month_day{ floor<days>(time) })
- sys_days(mozartBirthday))).count();
std::cout << "Birthday : " << mozartBirthday << "\n";
std::cout << "Deathday : " << mozartDeathday << "\n";
std::cout << "Years lived : " << yearsLived << "\n";
std::cout << "Days lived : " << daysLivedInt << "\n";
std::cout << "Years since birth : " << yearsSinceBirth << "\n";
}Output:
Simply requesting (UTC) time:
nowTime : 2022-07-07 15:04:58.0997165
Using formaters, current time zone and local time:
Time zone : Europe/Berlin
Date : 07.07.22 or 07.07.2022
Time : 17:04 or 17:04:58
TimeWithExactSec : 17:04:58.0997165
Calendar week : 27
DayOfYear : 188
Weekday : Thu or Thursday
Calculations with time and date:
FutureTimePoint : 08.07.2022 13:15:03
LeapYear : 2022 is no leapYear
Last day of month : 2022-07-31
Second Monday of month : 2022-07-11
Last Friday of month : 2022-07-29
DayOfYear : 188
DaysLeftInYear : 177
Calculations with Mozart:
Birthday : 1756-01-27
Deathday : 1791-12-05
Years lived : 35
Days lived : 13096
Years since birth : 266For format specifiers see: https://en.cppreference.com/w/cpp/chrono/system_clock/formatter#Format_specification
Measuring execution time
Method to watch the execution time of a given void function:
using milliseconds = std::chrono::duration<double, std::milli>;
milliseconds MeasureDuration(void(*func)())
{
auto timeBefore{ std::chrono::system_clock::now() };
// call given void function
func();
auto timeAfter{ std::chrono::system_clock::now() };
return milliseconds{ timeAfter - timeBefore };
}Dummy method which needs some time:
void DoSomething()
{
std::this_thread::sleep_for(std::chrono::milliseconds(123));
}Client code:
auto neededMilliSec = MeasureDuration(DoSomething);
std::cout << std::format("Needed execution time = {}", neededMilliSec);
Output:
Needed execution time = 133.112msGeneral infos
std::chrono::system_clock:
for working with time and date, the wall clock time (see example above), it is not guaranteed to be monotonic (i.e. the time ticks may occure with some irregularity)
std::chrono::steady_clock:
provides more reliable monotonic ticks for timer events, cannot be used for calendar time
std::chrono::high_resolution_clock
not recommended for general purpose use, may be an alias for one of the above clocks
For more info about time and date see also http://www.gerald-fahrnholz.eu/sw/display_contents.php?file_name=c11.htm#headLine_26