php测试代码执行时间的类

<?php
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); 
$start = floatval($StartMicro) + $StartSecond; 
$stop = floatval($StopMicro) + $StopSecond; 
$this->TimeSpent = $stop - $start; 
return round($this->TimeSpent,8)."秒"; 
}
} // end function spent(); 

} //end class timer;

$timer = new timer; 
$timer->start();
//测试代码

$timer->stop();
echo "</br>运行时间为: ".$timer->spent();
unset($timer);
?>