- print_r: documentation ( source)
- strtotime: documentation ( source)
<?php
$start = strtotime('20016-02-05');
$end = strtotime('2016-04-05');
$start_m = new DateTime($_GET["fecha1"]);
$end_m = new DateTime($_GET["fecha2"]);
$start_m->modify('first day of this month');
$end_m->modify('first day of next month');
$interval = DateInterval::createFromDateString('1 month');
$period = new DatePeriod($start_m, $interval, $end_m);
print_r($date_range_m);