php fileatime?取不到上次访问时间怎么办？

php fileatime $file='image/open1.txt';
$fopen=fopen($file,'r');
$content=fread($fopen,filesize($file));
echo $content;
date_default_timezone_set('Asia/Chongqing');
echo date("Y年m月d日 H:i:s",fileatime($file));
fclose（$file）;
?>
不管刷新、重新访问页面多少次，页面显示时间2013年12月05日 20:03:31总是不变。
这是为什么呢？

回复讨论(解决方案)

http://php.net/manual/en/function.fileatime.php

Note:
The atime of a file is supposed to change whenever the data blocks of a file are being read. This can be costly performance-wise when an application regularly accesses a very large number of files or directories.
Some Unix filesystems can be mounted with atime updates disabled to increase the performance of such applications; USENET news spools are a common example. On such filesystems this function will be useless.

不同的文件系统使用都会不同的..

可以试下clearstatcache() 清除下缓存再读

你代码写的有问题，清楚缓存，访问时间还是没有变化。