204 lines
5.5 KiB
Groff
204 lines
5.5 KiB
Groff
.\" Copyright (c) 1997 Wolfgang Helbig
|
|
.\" All rights reserved.
|
|
.\"
|
|
.\" Redistribution and use in source and binary forms, with or without
|
|
.\" modification, are permitted provided that the following conditions
|
|
.\" are met:
|
|
.\" 1. Redistributions of source code must retain the above copyright
|
|
.\" notice, this list of conditions and the following disclaimer.
|
|
.\" 2. Redistributions in binary form must reproduce the above copyright
|
|
.\" notice, this list of conditions and the following disclaimer in the
|
|
.\" documentation and/or other materials provided with the distribution.
|
|
.\"
|
|
.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
|
|
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
|
|
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
|
|
.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
|
|
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
|
|
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
|
|
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
|
|
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
|
|
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
|
|
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
|
|
.\" SUCH DAMAGE.
|
|
.\"
|
|
.\" $FreeBSD$
|
|
.\"
|
|
.Dd November 29, 1997
|
|
.Dt CALENDAR 3
|
|
.Os
|
|
.Sh NAME
|
|
.Nm easterg ,
|
|
.Nm easterog ,
|
|
.Nm easteroj ,
|
|
.Nm gdate ,
|
|
.Nm jdate ,
|
|
.Nm ndaysg ,
|
|
.Nm ndaysj ,
|
|
.Nm week ,
|
|
.Nm weekday
|
|
.Nd Calendar arithmetic for the Christian era
|
|
.Sh LIBRARY
|
|
.Lb libcalendar
|
|
.Sh SYNOPSIS
|
|
.In calendar.h
|
|
.Ft struct date *
|
|
.Fn easterg "int year" "struct date *dt"
|
|
.Ft struct date *
|
|
.Fn easterog "int year" "struct date *dt"
|
|
.Ft struct date *
|
|
.Fn easteroj "int year" "struct date *dt"
|
|
.Ft struct date *
|
|
.Fn gdate "int nd" "struct date *dt"
|
|
.Ft struct date *
|
|
.Fn jdate "int nd" "struct date *dt"
|
|
.Ft int
|
|
.Fn ndaysg "struct date *dt"
|
|
.Ft int
|
|
.Fn ndaysj "struct date *dt"
|
|
.Ft int
|
|
.Fn week "int nd" "int *year"
|
|
.Ft int
|
|
.Fn weekday "int nd"
|
|
.Sh DESCRIPTION
|
|
These functions provide calendar arithmetic for a large range of years,
|
|
starting at March 1st, year zero (i.e., 1 B.C.) and ending way beyond
|
|
year 100000.
|
|
.Pp
|
|
Programs should be linked with
|
|
.Fl lcalendar .
|
|
.Pp
|
|
The functions
|
|
.Fn easterg ,
|
|
.Fn easterog
|
|
and
|
|
.Fn easteroj
|
|
store the date of Easter Sunday into the structure pointed at by
|
|
.Fa dt
|
|
and return a pointer to this structure.
|
|
The function
|
|
.Fn easterg
|
|
assumes Gregorian Calendar (adopted by most western churches after 1582) and
|
|
the functions
|
|
.Fn easterog
|
|
and
|
|
.Fn easteroj
|
|
compute the date of Easter Sunday according to the orthodox rules
|
|
(Western churches before 1582, Greek and Russian Orthodox Church
|
|
until today).
|
|
The result returned by
|
|
.Fn easterog
|
|
is the date in Gregorian Calendar, whereas
|
|
.Fn easteroj
|
|
returns the date in Julian Calendar.
|
|
.Pp
|
|
The functions
|
|
.Fn gdate ,
|
|
.Fn jdate ,
|
|
.Fn ndaysg
|
|
and
|
|
.Fn 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.
|
|
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.
|
|
.Pp
|
|
The
|
|
.Fn gdate
|
|
and
|
|
.Fn jdate
|
|
functions
|
|
store the date corresponding to the day number
|
|
.Fa nd
|
|
into the structure pointed at by
|
|
.Fa dt
|
|
and return a pointer to this structure.
|
|
.Pp
|
|
The
|
|
.Fn ndaysg
|
|
and
|
|
.Fn ndaysj
|
|
functions
|
|
return the day number of the date pointed at by
|
|
.Fa dt .
|
|
.Pp
|
|
The
|
|
.Fn gdate
|
|
and
|
|
.Fn ndaysg
|
|
functions
|
|
assume Gregorian Calendar after October 4, 1582 and Julian Calendar before,
|
|
whereas
|
|
.Fn jdate
|
|
and
|
|
.Fn ndaysj
|
|
assume Julian Calendar throughout.
|
|
.Pp
|
|
The two calendars differ by the definition of the leap year.
|
|
The
|
|
Julian Calendar says every year that is a multiple of four is a
|
|
leap year.
|
|
The Gregorian Calendar excludes years that are multiples of
|
|
100 and not multiples of 400.
|
|
This means the years 1700, 1800, 1900, 2100 are not leap years
|
|
and the year 2000 is
|
|
a leap year.
|
|
The new rules were inaugurated on October 4, 1582 by deleting ten
|
|
days following this date.
|
|
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.
|
|
.Pp
|
|
The function
|
|
.Fn week
|
|
returns the number of the week which contains the day numbered
|
|
.Fa nd .
|
|
The argument
|
|
.Fa *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.
|
|
.Pp
|
|
The function
|
|
.Fn weekday
|
|
returns the weekday (Mo = 0 ..\& Su = 6) of the day numbered
|
|
.Fa nd .
|
|
.Pp
|
|
The structure
|
|
.Fa date
|
|
is defined in
|
|
.In calendar.h .
|
|
It contains these fields:
|
|
.Bd -literal -offset indent
|
|
int y; /\(** year (0000 - ????) \(**/
|
|
int m; /\(** month (1 - 12) \(**/
|
|
int d; /\(** day of month (1 - 31) \(**/
|
|
.Ed
|
|
.Pp
|
|
The year zero is written as "1 B.C." by historians and "0" by astronomers
|
|
and in this library.
|
|
.Sh SEE ALSO
|
|
.Xr ncal 1 ,
|
|
.Xr strftime 3
|
|
.Sh STANDARDS
|
|
The week number conforms to ISO 8601: 1988.
|
|
.Sh HISTORY
|
|
The
|
|
.Nm calendar
|
|
library first appeared in
|
|
.Fx 3.0 .
|
|
.Sh AUTHORS
|
|
This manual page and the library was written by
|
|
.An Wolfgang Helbig Aq helbig@FreeBSD.org .
|
|
.Sh BUGS
|
|
The library was coded with great care so there are no bugs left.
|