std::chrono::operator/(calendar) - cppreference.com
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    std::chrono::operator/(calendar)

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    Date and time library
    Time point
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    Duration
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    Clocks
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    Time of day
    (C++20)(C++20)
    (C++20)(C++20)
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    Calendar
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    (C++20)
    (C++20)
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    (C++20)(C++20)
    chrono I/O
    (C++20)

     

    These operator/ overloads provide a conventional syntax for the creation of Proleptic Gregorian calendar dates.

    For creation of a full date, any of the following three orders are accepted:

    • year/month/day,
    • month/day/year,
    • day/month/year.

    In each case day can replaced with one of:

    • std::chrono::last, for the last day of the month;
    • weekday[i], for the ith weekday of the month;
    • weekday[std::chrono::last], for the last weekday of the month.

    A plain integer is accepted if its meaning is unambiguous from the types of other operands: 2005y/4/5 is allowed, but 5/April/2005 is not.

    Partial-date types (year_month, month_day, etc.) can be created by not applying the second operator/ in any of the three orders.

    Return value

    1) std::chrono::year_month(y, m)
    2) std::chrono::year_month(y, std::chrono::month(m))
    3,6) std::chrono::month_day(m, d)
    4) std::chrono::month_day(m, std::chrono::day(d))
    5,7) std::chrono::month_day(std::chrono::month(m), d)
    8,10) std::chrono::month_day_last(m)
    9,11) std::chrono::month_day_last(std::chrono::month(m))
    12,14) std::chrono::month_weekday(m, wdi)
    13,15) std::chrono::month_weekday(std::chrono::month(m), wdi)
    16,18) std::chrono::month_weekday_last(m, wdl)
    17,19) std::chrono::month_weekday_last(std::chrono::month(m), wdl)
    20) std::chrono::year_month_day(ym.year(), ym.month(), d)
    21) std::chrono::year_month_day(ym.year(), ym.month(), std::chrono::day(d))
    22,24) std::chrono::year_month_day(y, md.month(), md.day())
    23,25) std::chrono::year_month_day(std::chrono::year(y), md.month(), md.day())
    26) std::chrono::year_month_day_last(ym.year(), std::chrono::month_day_last(ym.month()))
    27,29) std::chrono::year_month_day_last(y, mdl)
    28,30) std::chrono::year_month_day_last(std::chrono::year(y), mdl)
    31) std::chrono::year_month_weekday(ym.year(), ym.month(), wdi)
    32,34) std::chrono::year_month_weekday(y, mwd.month(), mwd.weekday_indexed())
    33,35) std::chrono::year_month_weekday(std::chrono::year(y), mwd.month(), mwd.weekday_indexed())
    36) std::chrono::year_month_weekday_last(ym.year(), ym.month(), wdl)
    37,39) std::chrono::year_month_weekday_last(y, mwdl.month(), mwdl.weekday_last())
    38,40) std::chrono::year_month_weekday_last(std::chrono::year(y), mwdl.month(), mwdl.weekday_last())

    Example

    Run this code
    #include <chrono>
using namespace std::chrono;

constexpr auto ym{2021y/8};
static_assert(ym == year_month(year(2021), August));

constexpr auto md{9/15d};
static_assert(md == month_day(September, day(15)));

constexpr auto mdl{October/last};
static_assert(mdl == month_day_last(month(10)));

constexpr auto mw{11/Monday[3]};
static_assert(mw == month_weekday(November, Monday[3]));

constexpr auto mwdl{December/Sunday[last]};
static_assert(mwdl == month_weekday_last(month(12), weekday_last(Sunday)));

// Those 3 year/month/day orders that people actually use on this planet and beyond:
constexpr auto ymd{year(2021)/January/day(23)};
static_assert(ymd == month{1}/23/2021);
static_assert(ymd == day{23}/1/2021);
static_assert(ymd == year_month_day(2021y, month(January), 23d));

int main() {}