分享一个PHP代码的执行时间，精确到微秒级

<span>function  </span><span>microtime_float </span><span>()
</span><span>{
</span><span>list</span><span>( </span><span>$usec </span><span>,  </span><span>$sec </span><span>) </span><span>=  </span><span>explode </span><span>( </span><span>" " </span><span>,  </span><span>microtime </span><span>());
</span><span>$sec</span><span>=(string)</span><span>$sec</span><span>;
</span><span>$sec</span><span>=</span><span>substr</span><span>(</span><span>$sec</span><span>,</span><span>-</span><span>4</span><span>);
</span><span>return </span><span>(</span><span>(float) </span><span>$sec </span><span>+(float)</span><span>$usec</span><span>);
</span><span>}
这段代码只能计算到时间戳后四位的结果，大概就是一小时之内的执行时间，想要检测更多的话，只要
修改substr中的截取的长度，但是要注意哈，float最大只支持14位哦。
</span>