php输出全部gb2312编码内的汉字方法

<?php
$fp = fopen('t.txt', 'a');
for($area = 0xb0; $area <= 0xf7; $area++)
  for($pos = 0xa1; $pos <= 0xfe; $pos++)
    fwrite($fp, pack('CC', $area, $pos));
fclose($fp);
?>