CALENDAR(3)

✨ CALENDAR(3) ✨ — calendar arithmetic, but make it iconic 💅

okay so bestie, this page is from the Library Functions Manual, and it's literally all about calendar arithmetic for the Christian era 🎀. The manual name is CALENDAR(3) — iykyk.

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💖 NAME 💖

easterg, easterog, easteroj, gdate, jdate, ndaysg, ndaysj, week, weekday — Calendar arithmetic for the Christian era. yes, all of them, one big happy family 🫶

🌸 LIBRARY 🌸

Calendar Arithmetic Library (libcalendar, -lcalendar) — she's got her own lib, main character energy fr.

🦋 SYNOPSIS 🦋

#include <calendar.h>

struct date *
easterg(int year, struct date *dt);

struct date *
easterog(int year, struct date *dt);

struct date *
easteroj(int year, struct date *dt);

struct date *
gdate(int nd, struct date *dt);

struct date *
jdate(int nd, struct date *dt);

int
ndaysg(struct date *dt);

int
ndaysj(struct date *dt);

int
week(int nd, int *year);

int
weekday(int nd);

no cap, that's the whole lineup 💜

✨ DESCRIPTION ✨

So these functions give you calendar arithmetic over a huge range of years, starting at March 1st, year zero (that's 1 B.C. bestie) and running way beyond year 100000. like, literally beyond. 🌈

Programs should be linked with -lcalendar. don't forget or she won't link 🥲

The easterg(), easterog() and easteroj() functions store the date of Easter Sunday into the structure pointed at by dt and return a pointer to this structure. iconique.

• easterg() — assumes Gregorian Calendar (adopted by most western churches after 1582).
• easterog() and easteroj() — compute the date of Easter Sunday according to the orthodox rules (Western churches before 1582, Greek and Russian Orthodox Church until today).

and here's the lil plot twist 🙈: the result returned by easterog() is the date in Gregorian Calendar, whereas easteroj() returns the date in Julian Calendar. two different fits, same holiday.

The functions gdate(), jdate(), ndaysg() and ndaysj() provide conversions between the common "year, month, day" notation of a date and the "number of days" representation, which is better suited for calculations. because math said so 💅

The days are numbered from March 1st year 1 B.C., starting with zero, so the number of a day gives the number of days since March 1st, year 1 B.C. The conversions work for nonnegative day numbers only — so like, no negative vibes please ⭐

• gdate() and jdate() store the date corresponding to the day number nd into the structure pointed at by dt and return a pointer to this structure.
• ndaysg() and ndaysj() return the day number of the date pointed at by dt.

The gdate() and ndaysg() functions assume Gregorian Calendar after October 4, 1582 and Julian Calendar before, whereas jdate() and ndaysj() assume Julian Calendar throughout. consistency queens vs. timeline girlies, pick your fighter 🧚

🎀 the whole leap year situation 🎀

The two calendars differ by the definition of the leap year, and it's giving drama:

• The Julian Calendar says every year that is a multiple of four is a leap year. simple. unbothered.
• The Gregorian Calendar excludes years that are multiples of 100 and not multiples of 400. so the years 1700, 1800, 1900, 2100 are not leap years and the year 2000 is a leap year. periodt.

The new rules were inaugurated on October 4, 1582 by deleting ten days following this date. literally just deleted them 😭. Most catholic countries adopted the new calendar by the end of the 16th century, whereas others stayed with the Julian Calendar until the 20th century. The United Kingdom and their colonies switched on September 2, 1752. They already had to delete 11 days. eleven!! the audacity 💀

🌟 week() and weekday() 🌟

The function week() returns the number of the week which contains the day numbered nd. The argument *year is set with the year that contains (the greater part of) the week. The weeks are numbered per year starting with week 1, which is the first week in a year that includes more than three days of the year. Weeks start on Monday. This function is defined for Gregorian Calendar only — Julian girlies, sit this one out 🙈

The function weekday() returns the weekday (Mo = 0 .. Su = 6) of the day numbered nd. yes the range is exactly that, copy it down 📝

💜 struct date 💜

The structure date is defined in <calendar.h>. It contains these fields:

int y;          /∗ year (0000 - ????) ∗/
int m;          /∗ month (1 - 12) ∗/
int d;          /∗ day of month (1 - 31) ∗/

The year zero is written as "1 B.C." by historians and "0" by astronomers and in this library. so if someone says 1 B.C. and someone else says 0, they're literally talking about the same year, no cap 🫶

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🔥 SEE ALSO 🔥

ncal(1), strftime(3) — go read those too bestie, expand your horizons ✨

🌸 STANDARDS 🌸

The week number conforms to ISO 8601: 1988. she's certified 📜

🎀 HISTORY 🎀

The calendar library first appeared in FreeBSD 3.0. a legend was born 👑

💖 AUTHORS 💖

This manual page and the library was written by Wolfgang Helbig <helbig@FreeBSD.org>. thank you king 🫡

💀 BUGS 💀

The library was coded with great care so there are no bugs left. (that's what the manpage says, and honestly? we love the confidence 👑✨)

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and that's the whole page bestie 💅 — this one's from Debian, dated November 29, 1997, and she ate fr fr 🍓🦋💜