<?php

function dates_between(DateTime $start, DateTime $end, $format = 'm-d-Y') {
    $date = $start;
    $dates = array();
    $oneDay = new DateInterval('P1D');
    // push all dates between start and end to the result
    while(($date = $date->add($oneDay)) < $end) {
        $dates []= $date->format($format);
    }
    return $dates;
}

$now = new DateTime();
$nextWeek = new DateTime('+1 week');
var_dump(dates_between($now, $nextWeek));

?>

Fatal error: Class 'DateInterval' not found on line 6