PHP DateTime::modify adding and subtracting months
date, datetime, php
Solution
Why it's not a bug:
The current behavior is correct. The following happens internally:
`+1 month` increases the month number (originally 1) by one. This makes the date `2010-02-31`.
The second month (February) only has 28 days in 2010, so PHP auto-corrects this by just continuing to count days from February 1st. You then end up at March 3rd.
How to get what you want:
To get what you want is by: manually checking the next month. Then add the number of days next month has.
I hope you can yourself code this. I am just giving what-to-do.
PHP 5.3 way:
To obtain the correct behavior, you can use one of the PHP 5.3's new functionality that introduces the relative time stanza `first day of`. This stanza can be used in combination with `next month`, `fifth month` or `+8 months` to go to the first day of the specified month. Instead of `+1 month` from what you're doing, you can use this code to get the first day of next month like this:
<?php
$d = new DateTime( '2010-01-31' );
$d->modify( 'first day of next month' );
echo $d->format( 'F' ), "\n";
?>
This script will correctly output `February`. The following things happen when PHP processes this `first day of next month` stanza:
`next month` increases the month number (originally 1) by one. This makes the date 2010-02-31.
`first day of` sets the day number to `1`, resulting in the date 2010-02-01.
Problem
I've been working a lot with the `DateTime class` and recently ran into what I thought was a bug when adding months. After a bit of research, it appears that it wasn't a bug, but instead working as intended. According to the documentation found here: Example #2 Beware when adding or subtracting months ``` <?php $date = new DateTime('2000-12-31'); $date->modify('+1 month'); echo $date->format('Y-m-d') . "\n"; $date->modify('+1 month'); echo $date->format('Y-m-d') . "\n"; ?> ``` ``` The above example will output: 2001-01-31 2001-03-03 ``` Can anyone justify why this isn't considered a bug? Furthermore does anyone have any elegant solutions to correct the issue and make it so +1 month will work as expected instead of as intended?