為什麼fwrite以後，fread不出來東西呢

為何fwrite以後，fread不出來東西呢。
$file = 'test.txt';
$fileHandle = fopen($file,'w+');
fwrite($fileHandle, 'Newly inserted text');
$fileContents = fread($fileHandle, filesize($file));
echo $fileContents;
fclose($fileHandle);

The manual says that if the w+ option is specified then the file is opened for reading and writing. From what I understand this means that I should be able to read from the file after writing to it. But the code above displays nothing after writing to the file. The file is chmodded 777. Can someone please explain to me why this is so :D

同問，為啥呢。
以w+模式開啟，應該是可讀，
可為何fwrite以後，fread不出來東西呢。

------解決方案--------------------
還真沒試過這樣，但可以猜想一下
1.指標問題
2.IO問題

想想寫完之後指標在哪？如果在檔案開頭，第二次寫入不是寫到第一次前面了？
檔案IO一般都涉及緩衝，兩次操作中間無間斷總會有想象不到的問題……

