microtime() 测试代码执行时间，提高编码效率

<?php
$b_time = microtime(true);
$a = array("","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","");
$count = ;
foreach ($a as $key => $value) {
 foreach ($a as $key => $value) {
  foreach ($a as $key => $value) {
   $b = ***************************************************************************************************************************************************************************************************************************************;
   //$count++;
  }
 }
}
$e_time = microtime(true);
$taketime = $e_time-$b_time;
//echo $taketime;
echo $taketime;
//3.5078401565552
//0.68016886711121
//15.500303983688
?>

它能精确到很细微的时间。不仅仅是秒。

在代码执行体首尾加上，可以检测执行的时间情况。

清晰代码的执行效率。