How to loop through months that have been already passed - php

Question

I have the following to loop through each month of the year. However, it seems to skip February.
$start = new DateTime('2015-01-01');
$start->modify('last day of this month');
$current = new DateTime('now');
$end = new DateTime('2018-01-01');
$interval = DateInterval::createFromDateString('1 month');
$period = new DatePeriod($start, $interval, $end);
$timestamps = array();
foreach ($period as $dt) {
$dt->modify('last day of this month');
echo 'C:' . $current->format('d F Y') . '<br>';
echo 'S:' . $start->format('d F Y') . '<br>';
echo 'D:' . $dt->format('d F Y') . '<br>';
echo '<br><br>';
}
However, the above outputs:
C:17 March 2015
S:31 January 2015
D:31 January 2015
C: 17 March 2015
S:31 January 2015
D:31 March 2015
C: 17 March 2015
S:31 January 2015
D:30 April 2015
Can anyone spot my mistake? I expected the second D to have a value of the 28 February 2015.
I just want a list of months that have already been passed.
Update
The problem highlighted by MLeFevre in the comments is that working with date intervals can be tricky. See Example #3 Beware when adding months http://php.net/manual/en/datetime.add.php.

Answer 1

Rather than use a DatePeriod, why not just use the modify method slightly differently like this:
$current = new DateTime('now');
$end = new DateTime('2018-01-01');
while($current < $end) {
$current->modify('last day of next month');
echo 'C:' . $current->format('d F Y') . '<br>';
}
In your question, you're firstly adding a month, then going to the end of that month. This doesn't work, as the length of each month varies.
Sample output:
C:30 April 2015
C:31 May 2015
C:30 June 2015
C:31 July 2015
C:31 August 2015
C:30 September 2015
C:31 October 2015
C:30 November 2015
C:31 December 2015
C:31 January 2016
C:29 February 2016
C:31 March 2016
// etc.
To loop from $start to $current, you could change the logic slightly like this:
$start = new DateTime('2015-01-31'); // start from end of month
$current = new DateTime('now');
do {
echo 'C:' . $start->format('d F Y') . '<br>';
} while($start->modify('last day of next month') < $current);
Output:
C:31 January 2015
C:28 February 2015

Answer 2

It happen because February has 28 days and your interval is 1 month (30 days). So it skips 30 days from 30 January to 2 March. Then it move to last day of March.
Change
$start->modify('last day of this month');
to
$start->modify('first day of this month');

Answer 3

Your first date is 31-Jan-2015. Since February has no 31st, it's going to March 3rd. Then you are telling it to go to the end of that month which is why you are getting the end of March after January and not February.