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Computes the week number of a date - ISO, Excel and Simple standards implemented. \begin{html}<span align="right" style="background-color:99FF99"><strong>Excel: WEEKNUM</strong></span>\end{html}

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Interface

#include <codecogs/units/date/weekofyear.h>

using namespace Units::Date;

int weekOfYear(int nDate, weekNumStd standard=wkn_ISO, int mode=1)

Overview

This function returns the week number within the Gregorian calendar only.

There are three main standards: \copydoc constants weekNumStd

Most implementations of these systems allow a week to start on Sunday rather than on a Monday, see Mode

The ISO 8601 solution is based on:

$a=\frac{14 - month}{12}$

(1)

$y=year -a$

(2)

$m=month+12a-2$

(3)

$d=\left ( Day + y + \frac{y}{4} - \frac{y}{100} + \frac{y}{400} + \frac{31m}{12} \right ) mod\ 7 +1$

(4)

where all divisions are an integer (rounding down) and d will contain the day of the week: 1 for Sunday, 2 for Monday, 3 for Tuesday, etc..

FUNCTION

weekOfYear

Computes the week number of a date using either the ISO, Excel or Simple methodologies.

References

www.faqs.org/faqs/calendars/faq/part3/
www.phys.uu.nl/~vgent/calendar/isocalendar.htm
www.proesite.com/timex/wkcalc.htm

Example 1

#include <stdio.h>
#include <codecogs/units/date/weekofyear.h>
#include <codecogs/units/date/dateymd.h>
#include <codecogs/units/date/date.h>
#include <codecogs/units/date/dayofweek.h>
#include <codecogs/units/date/weekday_str.h>

using namespace Units::Date;

int main()
{
  printf("\n    Date             Simple Excel ISO ");
  int adate=date("25 Dec 2002");
  for(int i=0;i<20;i++)
  {
    int d,m,y;
    dateYMD(adate+i, y, m, d);
    printf("\n %2d-%2d-%d %10s    %2d %2d %2d", d,m,y, weekday_str(dayOfWeek(adate+i)),
           weekOfYear(adate+i, wkn_Simple, 1),
           weekOfYear(adate+i, wkn_Excel, 1),
           weekOfYear(adate+i, wkn_ISO, 1));
  }
  return 0;
}

Output:

Date            Simple Excel ISO
25-12-2002  Wednesday    52 52 52
26-12-2002   Thursday    52 52 52
27-12-2002     Friday    52 52 52
28-12-2002   Saturday    52 52 52
29-12-2002     Sunday    52 53  1
30-12-2002     Monday    52 53  1
31-12-2002    Tuesday    53 53  1
1- 1-2003  Wednesday     1  1  1
2- 1-2003   Thursday     1  1  1
3- 1-2003     Friday     1  1  1
4- 1-2003   Saturday     1  1  1
5- 1-2003     Sunday     1  2  2
6- 1-2003     Monday     1  2  2
7- 1-2003    Tuesday     1  2  2
8- 1-2003  Wednesday     2  2  2
9- 1-2003   Thursday     2  2  2
10- 1-2003     Friday     2  2  2
11- 1-2003   Saturday     2  2  2
12- 1-2003     Sunday     2  3  3
13- 1-2003     Monday     2  3  3

Parameters

nDate

is a serial number of days from 24 November 4714 BC (1 January 4713BC in the Julian Calendar) - also known as the Julian Period.

standard

Default Value = wkn_ISO

mode

Default Value = 1

Author

Will Bateman (Oct 2004)