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');