计算页面执行时间

<? 
class timer
{ var $StartTime = 0;
var $StopTime = 0;
var $TimeSpent = 0;

function start(){
$this->StartTime = microtime();}
 function stop(){
 $this->StopTime　= microtime();}
 function spent(){
   if ($this->TimeSpent) {
   return $this->TimeSpent;
     } else {
$StartMicro = substr($this->StartTime,0,10);
$StartSecond = substr($this->StartTime,11,10);
$StopMicro　 = substr($this->StopTime,0,10);
$StopSecond　= substr($this->StopTime,11,10);
$start = doubleval($StartMicro) + $StartSecond;
$stop　= doubleval($StopMicro) + $StopSecond;
$this->TimeSpent = $stop - $start;
return substr($this->TimeSpent,0,8)."秒";
        }
     }// end function spent();
}//end class timer;
//例子
  $timer = new timer;
    $timer->start();
/*
你的代码放在此处
*/

$timer->stop();
echo "执行本SCRIPT共".$timer->spent();
?>