<?
$fp=fopen("x.txt","r");
$a=fread($fp,filesize("x.txt"));
fclose($fp);

$fp=fopen("x.txt","w");
fclose($fp);
?>

为什末执行这段代码，x.txt 就被清空了？难道$fp=fopen("x.txt","w");打开文件，不写东西就清空?