Welcome to an exciting journey through C++20's std::chrono library! Today, we'll dive into the fascinating world of handling time zones. šÆ
std::chrono š°ļøBefore we get started, let's understand what time zones are and why we need them. Time zones help us coordinate times across different geographical locations. In the context of std::chrono, we can handle time zones using zones and clocks.
std::chrono::zones šThe zones namespace in std::chrono provides functions for managing time zones. Here's how to create a zone:
#include <chrono>
#include <iostream>
int main() {
auto NewYork = std::chrono::zones::fixed_windows::from_utc(
std::chrono::hours{ -4 }, std::chrono::hours{ -3 });
std::cout << "New York's time zone: " << NewYork.name() << std::endl;
}In this example, we create a time zone for New York, which is 4 hours behind Coordinated Universal Time (UTC) during standard time and 3 hours behind during daylight saving time.
std::chrono::system_clock and std::chrono::zoned_time šNow that we have a time zone, let's learn about system_clock and zoned_time.
#include <chrono>
#include <iostream>
#include <zone>
int main() {
auto NewYork = std::chrono::zones::fixed_windows::from_utc(
std::chrono::hours{ -4 }, std::chrono::hours{ -3 });
auto now = std::chrono::system_clock::now();
auto NYTime = std::chrono::zoned_time<std::chrono::system_clock>::from_time_t(std::time_t(now.time_since_epoch().count()));
auto NYTimeInNewYork = NYTime.get_local_time<NewYork>();
std::cout << "Current time in UTC: " << now.time_since_epoch().count() << std::endl;
std::cout << "Current time in New York: " << NYTimeInNewYork << std::endl;
}In this example, we get the current time in UTC and convert it to the local time in New York using zoned_time and get_local_time.
Let's explore how to manipulate time zones using duration_cast and time_shift.
#include <chrono>
#include <iostream>
#include <zone>
int main() {
auto NewYork = std::chrono::zones::fixed_windows::from_utc(
std::chrono::hours{ -4 }, std::chrono::hours{ -3 });
auto now = std::chrono::system_clock::now();
auto NYTime = std::chrono::zoned_time<std::chrono::system_clock>::from_time_t(std::time_t(now.time_since_epoch().count()));
auto NYTimeInNewYork = NYTime.get_local_time<NewYork>();
auto oneHour = std::chrono::hours{ 1 };
auto shiftedNYTime = NYTimeInNewYork + oneHour;
auto shiftedNYTimeUTC = std::chrono::zoned_time<std::chrono::utc>::now().get_zones_et();
shiftedNYTimeUTC += std::chrono::hours{ -1 };
std::cout << "One hour ahead in New York: " << std::put_time(std::gmtime(&(shiftedNYTimeUTC.time_since_epoch().count())), "%F %T %z") << std::endl;
}In this example, we shift the local time in New York by one hour and convert it back to UTC.
What does `std::chrono::zones::fixed_windows::from_utc` do?
We hope you enjoyed this tutorial! Stay tuned for more exciting C++20 std::chrono lessons. š” Happy coding! š¤