Utilities library
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constexpr year_month_day_last( const std::chrono::year& y,
                               const std::chrono::month_day_last& mdl ) noexcept;
(since C++20)

Constructs a year_month_day_last object storing the year y and the month mdl.month(). The constructed object represents the last day of that year and month.

[edit] Notes

A year_month_day_last can also be created by combining a std::chrono::year_month with std::chrono::last using operator/.

[edit] Example

#include <chrono>
#include <iostream>
int main()
    std::cout << "All last days of months of a given year:\n";
    constexpr std::chrono::year year{2021};
    for (int i{1}; i <= 12; ++i)
        const std::chrono::month_day_last mdl{std::chrono::month(i) / std::chrono::last};
        const std::chrono::year_month_day_last ymdl{year, mdl};
        std::cout << ymdl << " day: " << << '\n';

Possible output:

All last days of months of a given year: 
2021/Jan/last day: 31
2021/Feb/last day: 28
2021/Mar/last day: 31
2021/Apr/last day: 30
2021/May/last day: 31
2021/Jun/last day: 30
2021/Jul/last day: 31
2021/Aug/last day: 31
2021/Sep/last day: 30
2021/Oct/last day: 31
2021/Nov/last day: 30
2021/Dec/last day: 31

[edit] See also

conventional syntax for Gregorian calendar date creation
(function) [edit]