php中计算程序运行时间的类代码

class Timer { 
private $StartTime = 0;//程序运行开始时间 
private $StopTime = 0;//程序运行结束时间 
private $TimeSpent = 0;//程序运行花费时间 
function start(){//程序运行开始 
$this->StartTime = microtime(); 
} 
function stop(){//程序运行结束 
$this->StopTime = microtime(); 
} 
function spent(){//程序运行花费的时间 
if ($this->TimeSpent) { 
return $this->TimeSpent; 
} else { 
list($StartMicro, $StartSecond) = explode(" ", $this->StartTime); 
list($StopMicro, $StopSecond) = explode(" ", $this->StopTime); 
$start = doubleval($StartMicro) + $StartSecond; 
$stop = doubleval($StopMicro) + $StopSecond; 
$this->TimeSpent = $stop - $start; 
return substr($this->TimeSpent,0,8)."秒";//返回获取到的程序运行时间差 
} 
} 
} 
$timer = new Timer(); 
$timer->start(); 
//...程序运行的代码 
$timer->stop(); 
echo "程序运行时间为:".$timer->spent();