php怎么计算一个月有几周

<?php
function get_weekinfo($month){
    $weekinfo = array();//创建一个空数组
    $end_date = date('d',strtotime($month.' +1 month -1 day'));//计算当前月有多少天
    for ($i=1; $i <$end_date ; $i=$i+7) {   //循环本月有多少周
        $w = date('N',strtotime($month.'-'.$i));  //计算第一天是周几
        $weekinfo[] = array(date('Y-m-d',strtotime($month.'-'.$i.' -'.($w-1).' days')),date('Y-m-d',strtotime($month.'-'.$i.' +'.(7-$w).' days')));
    }                                                    //当周开始时间                    //结束时间
    return $weekinfo;
}
print_r(get_weekinfo('2017-5'));

Array
(
    [0] => Array
        (
            [0] => 2017-05-01
            [1] => 2017-05-07
        )
    [1] => Array
        (
            [0] => 2017-05-08
            [1] => 2017-05-14
        )
    [2] => Array
        (
            [0] => 2017-05-15
            [1] => 2017-05-21
        )
    [3] => Array
        (
            [0] => 2017-05-22
            [1] => 2017-05-28
        )
    [4] => Array
        (
            [0] => 2017-05-29
            [1] => 2017-06-04
        )
)
?>