std::chrono -> Java's LocalDate, LocalDateTime and ZonedDateTime

[octopus-prime]

Channel

C++Weekly

Topics

A video about std::chrono. How to build something like Java's LocalDate, LocalDateTime and ZonedDateTime.

Length

10-20 minutes

[octopus-prime]

It's so confusing...

I just want

    void java() {
        LocalDateTime localDateTime = LocalDateTime.now();
        localDateTime = localDateTime.minusDays(1);
        boolean b = localDateTime.isBefore(localDateTime);
        int y = localDateTime.getYear();
        int m = localDateTime.getMonthValue();
        int d = localDateTime.getDayOfMonth();
        System.out.println(localDateTime);
    }

But how??

void cpp() {
    using LocalDateTime = std::chrono::local_time<std::chrono::system_clock::duration>;
    LocalDateTime localDateTime = std::chrono::system_clock::now(); // ?? broken
    localDateTime -= std::chrono::days{1};
    bool b = localDateTime < localDateTime;
    int y = localDateTime.year(); // ?? broken
    int m = localDateTime.month(); // ?? broken
    int d = localDateTime.day(); // ?? broken
    std::println("{}", localDateTime);
}

Is there any useful 'LocalDateTime' / 'LocalDate' type in c++?

[octopus-prime]

More confusion...

int main() {
    using LocalDate = std::chrono::year_month_day;

    LocalDate today; // how to get the current date?

    today.year();
    today.month();
    today.day();

    bool bd = today < today;
    today += std::chrono::days{1}; // broken

    std::println("{}", today);

    // --------

    using LocalTime = std::chrono::hh_mm_ss<std::chrono::system_clock::duration>;

    LocalTime now; // how to get the current time?

    now.hours();
    now.minutes();
    now.seconds();
    now.subseconds();

    bool bt = now < now; // broken
    now += std::chrono::seconds{1}; // broken

    std::println("{}", now);
}

If we remove the broken parts and compile and run the output is

32739-00-00 is not a valid date
00:00:00.000000

lol - how to use that suff??

[octopus-prime]

Here we go...

#include <boost/date_time/posix_time/posix_time.hpp>
#include <print>

int main() {
    using namespace boost::posix_time;

    auto now = microsec_clock::local_time();
    auto d = now.date().day();
    auto mo = now.date().month();
    auto y = now.date().year();
    auto h = now.time_of_day().hours();
    auto mi = now.time_of_day().minutes();
    auto s = now.time_of_day().seconds();
    auto b = now < now;

    now += seconds{1};

    std::println("{}", to_iso_extended_string(now));
}

But it's boost::date_time. And std::chrono ??

[octopus-prime]

Hmm

#include <chrono>
#include <print>

int main() {
    using namespace std::chrono;

    time_point now {system_clock::now()};

    now += seconds{1};
    bool b = now < now;

    year_month_day date {floor<days>(now)};
    auto d = date.day();
    auto mo = date.month();
    auto y = date.year();

    hh_mm_ss time {now - floor<days>(now)};
    auto h = time.hours();
    auto mi = time.minutes();
    auto s = time.seconds();
    auto ms = time.subseconds();
}

Pretty ugly

[LB--]

Check out the example on cppreference for std::chrono::zoned_time: https://en.cppreference.com/w/cpp/chrono/zoned_time