php判断某年的某月有多少天

<?php
header('Content-Type:text/html;Charset=utf-8');

$year = 2018;
$month = 2;
$last = getDaysInMonth($year, $month);

//把一个月分割成3部分
$a = $year . "-" . $month . "-1 00:00:00";
$b = $year . "-" . $month . "-10 23:59:59";
$c = $year . "-" . $month . "-11 00:00:00";
$d = $year . "-" . $month . "-20 23:59:59";
$e = $year . "-" . $month . "-21 00:00:00";
$f = $year . "-" . $month . "-$last 23:59:59";

print_r($a . " 至 " . $b);
echo "<br/>";
print_r($c . " 至 " . $d);
echo "<br/>";
print_r($e . " 至 " . $f);


/**
 * 判断某年的某月有多少天
 * @return [type] [description]
 */
function getDaysInMonth($year = '', $month = '')
{
    if (empty($year)) $year = date('Y');
    if (empty($month)) $month = date('m');
    if (in_array($month, array(1, 3, 5, 7, 8, '01', '03', '05', '07', '08', 10, 12))) {
        $text = '31';//月大
    } elseif ($month == 2 || $month == '02') {
        if (($year % 400 == 0) || (($year % 4 == 0) && ($year % 100 !== 0))) {//判断是否是闰年
            $text = '29';//闰年2月
        } else {
            $text = '28';//平年2月
        }
    } else {
        $text = '30';//月小
    }
    return $text;
}