计算两个时间相差的天，时，分，秒

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$d = "2012-05-22 15:30:10";
function shi_jian_cha($d,$d1)
{    
    $time = strtotime($d) - strtotime($d1);	
    $n_time = str_pad(floor($time/3600/24),2,0,STR_PAD_LEFT )."天".str_pad(floor($time%(24*3600)/3600),2,0,STR_PAD_LEFT )."小时".str_pad(floor($time%3600/60),2,0,STR_PAD_LEFT)."分".str_pad($time%3600%60, 2, 0, STR_PAD_LEFT)."秒";
    return $n_time;
}