DateTime addition of interval gives wrong ans

Question

2While trying to get the next month by adding the +1 month in strtotime function as well DateTime class, its not giving right answer when start date time is 31 January 2011.

<?php

$StartDateline = new DateTime("31 January 2011");

echo date('Y-m-d', $StartDateline->getTimestamp());
echo "<br>";
$EndDateline = $StartDateline->add(new DateInterval("P1M"));//strtotime("+1 month", $startDateline);

echo date('Y-m-d', $EndDateline->getTimestamp());

echo "<br>";

?>

Output is :

2011-01-31
2011-03-03

Expected result should be following or how should I get the following out put :

2011-01-31
2011-02-28

Thanks

Why on earth would you expect 1 month to add 2 months to your date? — Hanky Panky, Sep 16 '14 at 07:44
your expected result is more than 25 days beyond what it should be — Hanky Panky, Sep 16 '14 at 07:44
Mistakenly I have written `2011-03-28` it should be `2011-02-28`. Thanks @YUNOWORK — krishna Prasad, Sep 16 '14 at 08:02
@krishna I've updated my answer, please review and accpet if it helped you. — Nitsan Baleli, Sep 16 '14 at 13:44

score 0 · Answer 1 · answered Sep 16 '14 at 07:47

0

instead of specifying month specify date.

new DateInterval("P#D")// # no. of days.

or you can use modify.see here:http://php.net/manual/en/datetime.modify.php

answered Sep 16 '14 at 07:47

Suchit kumar

11,809
3
22
44

score 0 · Accepted Answer · edited May 23 '17 at 10:33

This works:

<?php
    $StartDateline = new DateTime("31 January 2011");
    echo date('Y-m-d', $StartDateline->getTimestamp());
    echo "<br>";

    $test = $StartDateline->modify('last day of next month');
    echo date('Y-m-d', $test->getTimestamp());
    echo "<br>";
?>

result:

2011-01-31
2011-02-28

Here's a similar answer that exaplains why your way doesn't give the wanted output.

PHP docs on DateTime::modify method

edit: I understand now that you don't need the last day of next month, but the same day of next month. I found this code working:

function addMonthsToTime($numMonths = 1, $timeStamp = null){
    $timeStamp === null and $timeStamp = time();//Default to the present
    $newMonthNumDays =  date('d',strtotime('last day of '.$numMonths.' months', $timeStamp));//Number of days in the new month
    $currentDayOfMonth = date('d',$timeStamp);

    if($currentDayOfMonth > $newMonthNumDays){
      $newTimeStamp = strtotime('-'.($currentDayOfMonth - $newMonthNumDays).' days '.$numMonths.' months', $timeStamp);
    } else {
    $newTimeStamp = strtotime($numMonths.' months', $timeStamp);
    }

    return $newTimeStamp;
}

$timestamp = strtotime('2011-01-01');
echo date('m/d/Y', addMonthsToTime(1, $timestamp));
//02/01/2011

$timestamp = strtotime('2011-01-31');
echo date('m/d/Y', addMonthsToTime(1, $timestamp));
//02/28/2011

taken from this comment section on PHP's Relative Formats doc page.

I want in general, Like 30 or 31 Jan 2011 goes to 28 Feb 2011, 1 Jan 2011 should goes to 1 Feb 2011 — krishna Prasad, Sep 16 '14 at 08:16
If my answer is correct consider accepting it.If your question changed, please edit your question above. — Nitsan Baleli, Sep 16 '14 at 08:22
@NitsanBaleli: wyh would you even mix `date()` function and `DateTime` object? — Glavić, Sep 16 '14 at 18:28

score 0 · Answer 3 · edited May 23 '17 at 11:55

0

The current behavior of PHP DateTime is not wrong. What's really happening is

+1 month increases the month number (originally 1) by one. This makes the date 2011-03-03.
The second month (February) only has 28 days in 2011, so PHP auto-corrects this by just continuing to count days from February 1st. You then end up at March 3rd. January 31 + 31 days (1 month) = March 3 ( since there are only 28 days in february)

See @shamittomar

To get the expected answer you should use the number of days

That's why in the PHP Manual DateTime it says beware when adding months.

So just replace P1M with P28D to get desired result

$EndDateline = $StartDateline->add(new DateInterval("P28D"));

See DEMO

edited May 23 '17 at 11:55

Community

1
1

answered Sep 16 '14 at 07:56

John Robertson

1,486
13
16

Since I want to increase a month in general, I don't know the date is 31 Jan or 30 Jan. or 1 Jan 2011. I just want to increase one month e.g : * 1 Jan 2011 should goes to 1 Feb 2011, * 30 or 31 Jan 2011 both should goes 28 Feb 2011 and so on. I want it is general. – krishna Prasad Sep 16 '14 at 08:07
@krishna you can do conditional statements with that one – John Robertson Sep 16 '14 at 08:13
Okay, Is it not possible through `Datetime` methods or `strtotime` function ?? – krishna Prasad Sep 16 '14 at 08:15
@krishna You can use P1M but there's a catch when february comes. That's why it is up to you to consider that and in the manual http://php.net/manual/en/datetime.add.php example three it says Beware when adding months. So use conditional statements to check the month. Check http://stackoverflow.com/questions/3602405/php-datetimemodify-adding-and-subtracting-months or study $d->modify( 'first day of next month' ) – John Robertson Sep 16 '14 at 08:25

score 0 · Answer 4 · edited May 23 '17 at 12:26

John Robertson already explained why you get the result you get. The output is correct, because when you add +1 month to 31.1. it will become 31.2. which is 3 days more than 28.2., so correct results is 3.3..

For your needs, you will need a custom script, what will handle carry-over-day your way, for example:

$start = new DateTime('31 January 2011');

$new   = clone $start;
$new->modify('first day of next month'); 
$newDay = ($start->format('j') > $new->format('t') ? $new->format('t') : $start->format('j')) - 1;
$new->modify("+{$newDay} days");

echo $start->format('Y-m-d'), " > ", $new->format('Y-m-d');

demo

Thanks for your response, it really help to out from the problem. — krishna Prasad, Sep 22 '14 at 11:36

DateTime addition of interval gives wrong ans

4 Answers4