I have tried to solve this question for years now, I thought I found a shorter solution but had to come back again to the long story. This function gives back the right ISO week notation:
/**
* calcweek["2018-12-31"] => 1901
* This function calculates the production weeknumber according to the start on
* monday and with at least 4 days in the new year. Given that the $date has
* the following format Y-m-d then the outcome is and integer.
*
* @author M.S.B. Bachus
*
* @param date-notation PHP "Y-m-d" showing the data as yyyy-mm-dd
* @return integer
**/
function calcweek[$date] {
// 1. Convert input to $year, $month, $day
$dateset = strtotime[$date];
$year = date["Y", $dateset];
$month = date["m", $dateset];
$day = date["d", $dateset];
$referenceday = getdate[mktime[0,0,0, $month, $day, $year]];
$jan1day = getdate[mktime[0,0,0,1,1,$referenceday[year]]];
// 2. check if $year is a leapyear
if [ [$year%4==0 && $year%100!=0] || $year%400==0] {
$leapyear = true;
} else {
$leapyear = false;
}
// 3. check if $year-1 is a leapyear
if [ [[$year-1]%4==0 && [$year-1]%100!=0] || [$year-1]%400==0 ] {
$leapyearprev = true;
} else {
$leapyearprev = false;
}
// 4. find the dayofyearnumber for y m d
$mnth = array[0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334];
$dayofyearnumber = $day + $mnth[$month-1];
if [ $leapyear && $month > 2 ] { $dayofyearnumber++; }
// 5. find the jan1weekday for y [monday=1, sunday=7]
$yy = [$year-1]%100;
$c = [$year-1] - $yy;
$g = $yy + intval[$yy/4];
$jan1weekday = 1+[[[[intval[$c/100]%4]*5]+$g]%7];
// 6. find the weekday for y m d
$h = $dayofyearnumber + [$jan1weekday-1];
$weekday = 1+[[$h-1]%7];
// 7. find if y m d falls in yearnumber y-1, weeknumber 52 or 53
$foundweeknum = false;
if [ $dayofyearnumber 4 ] {
$yearnumber = $year - 1;
if [ $jan1weekday = 5 || [ $jan1weekday = 6 && $leapyearprev ]] {
$weeknumber = 53;
} else {
$weeknumber = 52;
}
$foundweeknum = true;
} else {
$yearnumber = $year;
}
// 8. find if y m d falls in yearnumber y+1, weeknumber 1
if [ $yearnumber == $year && !$foundweeknum] {
if [ $leapyear ] {
$i = 366;
} else {
$i = 365;
}
if [ [$i - $dayofyearnumber] < [4 - $weekday] ] {
$yearnumber = $year + 1;
$weeknumber = 1;
$foundweeknum = true;
}
}
// 9. find if y m d falls in yearnumber y, weeknumber 1 through 53
if [ $yearnumber == $year && !$foundweeknum ] {
$j = $dayofyearnumber + [7 - $weekday] + [$jan1weekday - 1];
$weeknumber = intval[ $j/7 ];
if [ $jan1weekday > 4 ] { $weeknumber--; }
}
// 10. output iso week number [YYWW]
return [$yearnumber-2000]*100+$weeknumber;
}
I found out that my short solution missed the 2018-12-31 as it gave back 1801 instead of 1901. So I had to put in this long version which is correct.
[PHP 4, PHP 5, PHP 7, PHP 8]
date — Format a Unix timestamp
Description
date[string $format, ?int $timestamp = null]: string
Parameters
formatFormat accepted by DateTimeInterface::format[].
timestamp The optional timestamp parameter is an int Unix timestamp that defaults to the current local time if timestamp is omitted or null. In other words, it defaults to the value of
time[].
Return Values
Returns a formatted date string. If a non-numeric value is used for timestamp, false is returned and an E_WARNING level error is emitted.
Errors/Exceptions
Every call to a date/time function will generate a
E_WARNING if the time zone is not valid. See also date_default_timezone_set[]
Changelog
| 8.0.0 | timestamp is nullable now.
|
Examples
Example #1 date[] examples
You can prevent a recognized character in the format string from being expanded by escaping it with a preceding backslash. If the character with a backslash is already a special sequence, you may need to also escape the backslash.
Example #2 Escaping characters in date[]
It is possible to use date[] and mktime[] together to find dates in the future or the past.
Example #3 date[] and mktime[] example
Note:
This can be more reliable than simply adding or subtracting the number of seconds in a day or month to a timestamp because of daylight saving time.
Some examples of date[] formatting. Note that you should escape any other characters, as any which currently have a special meaning will produce undesirable results, and other characters may be assigned meaning in future PHP versions. When escaping, be sure to use single quotes to prevent characters like \n from becoming newlines.
Example #4 date[] Formatting
To format dates in other languages, IntlDateFormatter::format[] can be used instead of date[].
Notes
Note:
To generate a timestamp from a string representation of the date, you may be able to use strtotime[]. Additionally, some databases have functions to convert their date formats into timestamps [such as MySQL's » UNIX_TIMESTAMP function].
See Also
- DateTimeImmutable::__construct[] - Returns new DateTimeImmutable object
- DateTimeInterface::format[] - Returns date formatted according to given format
- gmdate[] - Format a GMT/UTC date/time
- idate[] - Format a local time/date part as integer
- getdate[] - Get date/time information
- getlastmod[] - Gets time of last page modification
- mktime[] - Get Unix timestamp for a date
- IntlDateFormatter::format[] - Format the date/time value as a string
- time[] - Return current Unix timestamp
- Predefined DateTime Constants
There are no user contributed notes for this page.