PHP strtotime +1 month behaviour

问题:

I know about the unwanted behaviour of PHP's function

strtotime

For example, when adding a month (+1 month) to dates like: 31.01.2011 -> 03.03.2011

I know it's not officially a PHP bug, and that this solution has some arguments behind it, but at least for me, this behavior has caused a lot waste of time (in the past and present) and I personally hate it.

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What I found even stranger is that for example in:

MySQL: DATE_ADD('2011-01-31', INTERVAL 1 MONTH) returns 2011-02-28 or

C# where new DateTime(2011, 01, 31).AddMonths(1); will return 28.02.2011

wolframalpha.com giving 31.01.2013 + 1 month as input; will return Thursday, February 28, 2013

It sees to me that others have found a more decent solution to the stupid question that I saw alot in PHP bug reports "what day will it be, if I say we meet in a month from now" or something like that. The answer is: if 31 does not exists in next month, get me the last day of that month, but please stick to next month.

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So MY QUESTION IS: is there a PHP function (written by somebody) that resolves this not officially recognized bug? As I don't think I am the only one who wants another behavior when adding / subtracting months.

I am particulary interested in solutions what also work not just for the end of the month, but a complete replacement of strtotime. Also the case strotime +n months should be also dealt with.

Happy coding!

回答1:

Here's the algorithm you can use. It should be simple enough to implement yourself.

• Have the original date and the +1 month date in variables
• Extract the month part of both variables
• If the difference is greater than 1 month (or if the original is December and the other is not January) change the latter variable to the last day of the next month. You can use for example t in date() to get the last day: date( 't.m.Y' )

回答2:

what you need is to tell PHP to be smarter

$the_date = strtotime('31.01.2011');
echo date('r', strtotime('last day of next month', $the_date));

$the_date = strtotime('31.03.2011');
echo date('r', strtotime('last day of next month', $the_date));

assuming you are only interesting on the last day of next month

reference - http://www.php.net/manual/en/datetime.formats.relative.php

回答3:

PHP devs surely don't consider this as bug. But in strtotime's docs there are few comments with solutions for your problem (look for 28th Feb examples ;)), i.e. this one extending DateTime class:

<?php
// this will give us 2010-02-28 ()
echo PHPDateTime::DateNextMonth(strftime('%F', strtotime("2010-01-31 00:00:00")), 31);
?>

Class PHPDateTime:

<?php
/**
 * IA FrameWork
 * @package: Classes & Object Oriented Programming
 * @subpackage: Date & Time Manipulation
 * @author: ItsAsh <ash at itsash dot co dot uk>
 */

final class PHPDateTime extends DateTime {

    // Public Methods
    // ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

    /**
     * Calculate time difference between two dates
     * ...
     */

    public static function TimeDifference($date1, $date2)
        $date1 = is_int($date1) ? $date1 : strtotime($date1);
        $date2 = is_int($date2) ? $date2 : strtotime($date2);

        if (($date1 !== false) && ($date2 !== false)) {
            if ($date2 >= $date1) {
                $diff = ($date2 - $date1);

                if ($days = intval((floor($diff / 86400))))
                    $diff %= 86400;
                if ($hours = intval((floor($diff / 3600))))
                    $diff %= 3600;
                if ($minutes = intval((floor($diff / 60))))
                    $diff %= 60;

                return array($days, $hours, $minutes, intval($diff));
            }
        }

        return false;
    }

    /**
     * Formatted time difference between two dates
     *
     * ...
     */

    public static function StringTimeDifference($date1, $date2) {
        $i = array();
        list($d, $h, $m, $s) = (array) self::TimeDifference($date1, $date2);

        if ($d > 0)
            $i[] = sprintf('%d Days', $d);
        if ($h > 0)
            $i[] = sprintf('%d Hours', $h);
        if (($d == 0) && ($m > 0))
            $i[] = sprintf('%d Minutes', $m);
        if (($h == 0) && ($s > 0))
            $i[] = sprintf('%d Seconds', $s);

        return count($i) ? implode(' ', $i) : 'Just Now';
    }

    /**
     * Calculate the date next month
     *
     * ...
     */

    public static function DateNextMonth($now, $date = 0) {
        $mdate = array(0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31);
        list($y, $m, $d) = explode('-', (is_int($now) ? strftime('%F', $now) : $now));

        if ($date)
            $d = $date;

        if (++$m == 2)
            $d = (($y % 4) === 0) ? (($d <= 29) ? $d : 29) : (($d <= 28) ? $d : 28);
        else
            $d = ($d <= $mdate[$m]) ? $d : $mdate[$m];

        return strftime('%F', mktime(0, 0, 0, $m, $d, $y));
    }

}
?>

回答4:

Had the same issue recently and ended up writing a class that handles adding/subtracting various time intervals to DateTime objects.
Here's the code:
https://gist.github.com/pavlepredic/6220041#file-gistfile1-php
I've been using this class for a while and it seems to work fine, but I'm really interested in some peer review. What you do is create a TimeInterval object (in your case, you would specify 1 month as the interval) and then call addToDate() method, making sure you set $preventMonthOverflow argument to true. The code will make sure that the resulting date does not overflow into next month.

Sample usage:

$int = new TimeInterval(1, TimeInterval::MONTH);
$date = date_create('2013-01-31');
$future = $int->addToDate($date, true);
echo $future->format('Y-m-d');

Resulting date is: 2013-02-28

回答5:

Here is an implementation of an improved version of Juhana's answer above:

<?php
function sameDateNextMonth(DateTime $createdDate, DateTime $currentDate) {
    $addMon = clone $currentDate;
    $addMon->add(new DateInterval("P1M"));

    $nextMon = clone $currentDate;
    $nextMon->modify("last day of next month");

    if ($addMon->format("n") == $nextMon->format("n")) {
        $recurDay = $createdDate->format("j");
        $daysInMon = $addMon->format("t");
        $currentDay = $currentDate->format("j");
        if ($recurDay > $currentDay && $recurDay <= $daysInMon) {
            $addMon->setDate($addMon->format("Y"), $addMon->format("n"), $recurDay);
        }
        return $addMon;
    } else {
        return $nextMon;
    }
}

This version takes $createdDate under the presumption that you are dealing with a recurring monthly period, such as a subscription, that started on a specific date, such as the 31st. It always takes $createdDate so late "recurs on" dates won't shift to lower values as they are pushed forward thru lesser-valued months (e.g., so all 29th, 30th or 31st recur dates won't eventually get stuck on the 28th after passing thru a non-leap-year February).

Here is some driver code to test the algorithm:

$createdDate = new DateTime("2015-03-31");
echo "created date = " . $createdDate->format("Y-m-d") . PHP_EOL;

$next = sameDateNextMonth($createdDate, $createdDate);
echo "   next date = " . $next->format("Y-m-d") . PHP_EOL;

foreach(range(1, 12) as $i) {
    $next = sameDateNextMonth($createdDate, $next);
    echo "   next date = " . $next->format("Y-m-d") . PHP_EOL;
}

Which outputs:

created date = 2015-03-31
   next date = 2015-04-30
   next date = 2015-05-31
   next date = 2015-06-30
   next date = 2015-07-31
   next date = 2015-08-31
   next date = 2015-09-30
   next date = 2015-10-31
   next date = 2015-11-30
   next date = 2015-12-31
   next date = 2016-01-31
   next date = 2016-02-29
   next date = 2016-03-31
   next date = 2016-04-30

回答6:

I have solved it by this way:

$startDate = date("Y-m-d");
$month = date("m",strtotime($startDate));
$nextmonth = date("m",strtotime("$startDate +1 month"));
if((($nextmonth-$month) > 1) || ($month == 12 && $nextmonth != 1))
{
    $nextDate = date( 't.m.Y',strtotime("$initialDate +1 week"));
}else
{
    $nextDate = date("Y-m-d",strtotime("$initialDate +1 month"));
}
echo $nextDate;

回答7:

Somewhat similar to the Juhana's answer but more intuitive and less complications expected. Idea is like this:

1. Store original date and the +n month(s) date in variables
2. Extract the day part of both variables
3. If days do not match, subtract number of days from the future date

Plus side of this solution is that works for any date (not just the border dates) and it also works for subtracting months (by putting - instead of +). Here is an example implementation:

$start = mktime(0,0,0,1,31,2015);
for ($contract = 0; $contract < 12; $contract++) {
    $end = strtotime('+ ' . $contract . ' months', $start);
    if (date('d', $start) != date('d', $end)) { 
        $end = strtotime('- ' . date('d', $end) . ' days', $end);
    }
    echo date('d-m-Y', $end) . '|';
}

And the output is following:

31-01-2015|28-02-2015|31-03-2015|30-04-2015|31-05-2015|30-06-2015|31-07-2015|31-08-2015|30-09-2015|31-10-2015|30-11-2015|31-12-2015|

回答8:

function ldom($m,$y){

     //return tha last date of a given month based on the month and the year 
    //(factors in leap years)

    $first_day= strtotime (date($m.'/1/'.$y));
    $next_month = date('m',strtotime ( '+32 day' , $first_day)) ;   
    $last_day= strtotime ( '-1 day' , strtotime (date($next_month.'/1/'.$y)) ) ;
    return $last_day;       

}