function get_day( $date )  
{
    $tem = explode('-' , $date); //切割日期 得到年份和月份
    $year = $tem['0'];
    $month = $tem['1'];
    if( in_array($month , array( 1 , 3 , 5 , 7 , 8 , 01 , 03 , 05 , 07 , 08 , 10 , 12)))
    {
      // $text = $year.'年的'.$month.'月有31天';
      $text = '31';
    }
    elseif( $month == 2 )
    {
      if ( $year%400 == 0 || ($year%4 == 0 && $year%100 !== 0) )    //判断是否是闰年
      {
        // $text = $year.'年的'.$month.'月有29天';
        $text = '29';
      }
      else{
        // $text = $year.'年的'.$month.'月有28天';
        $text = '28';
      }
    }
    else{
      // $text = $year.'年的'.$month.'月有30天';
      $text = '30';
    }
    return $text;
}
echo get_day('2016-8-1');

/**
* 获取当月天数
* @param $date 
* @param $rtype 1天数 2具体日期数组
* @return 
*/
function get_day( $date ,$rtype = '1')  
{
    $tem = explode('-' , $date);    //切割日期 得到年份和月份
    $year = $tem['0'];
    $month = $tem['1'];
    if( in_array($month , array( 1 , 3 , 5 , 7 , 8 , 01 , 03 , 05 , 07 , 08 , 10 , 12)))
    {
      // $text = $year.'年的'.$month.'月有31天';
      $text = '31';
    }
    elseif( $month == 2 )
    {
      if ( $year%400 == 0 || ($year%4 == 0 && $year%100 !== 0) )    //判断是否是闰年
      {
        // $text = $year.'年的'.$month.'月有29天';
        $text = '29';
      }
      else{
        // $text = $year.'年的'.$month.'月有28天';
        $text = '28';
      }
    }
    else{
      // $text = $year.'年的'.$month.'月有30天';
      $text = '30';
    }
    if ($rtype == '2') {
      for ($i = 1; $i <= $text ; $i ++ ) {
        $r[] = $year."-".$month."-".$i;
      }
    } else {
      $r = $text;
    }
    return $r;
}
var_dump(get_day('2016-8-1','2'));

array(31) {
 [0]=>
 string(8) "2016-8-1"
 [1]=>
 string(8) "2016-8-2"
 [2]=>
 string(8) "2016-8-3"
 [3]=>
 string(8) "2016-8-4"
 [4]=>
 string(8) "2016-8-5"
 [5]=>
 string(8) "2016-8-6"
 [6]=>
 string(8) "2016-8-7"
 [7]=>
 string(8) "2016-8-8"
 [8]=>
 string(8) "2016-8-9"
 [9]=>
 string(9) "2016-8-10"
 [10]=>
 string(9) "2016-8-11"
 [11]=>
 string(9) "2016-8-12"
 [12]=>
 string(9) "2016-8-13"
 [13]=>
 string(9) "2016-8-14"
 [14]=>
 string(9) "2016-8-15"
 [15]=>
 string(9) "2016-8-16"
 [16]=>
 string(9) "2016-8-17"
 [17]=>
 string(9) "2016-8-18"
 [18]=>
 string(9) "2016-8-19"
 [19]=>
 string(9) "2016-8-20"
 [20]=>
 string(9) "2016-8-21"
 [21]=>
 string(9) "2016-8-22"
 [22]=>
 string(9) "2016-8-23"
 [23]=>
 string(9) "2016-8-24"
 [24]=>
 string(9) "2016-8-25"
 [25]=>
 string(9) "2016-8-26"
 [26]=>
 string(9) "2016-8-27"
 [27]=>
 string(9) "2016-8-28"
 [28]=>
 string(9) "2016-8-29"
 [29]=>
 string(9) "2016-8-30"
 [30]=>
 string(9) "2016-8-31"
}