(PHP 4 >= 4.2.0, PHP 5 < 5.1.0)
dio_truncate — 截断文件描述符 fd 为 offset 字节
$fd, int $offset): bool
dio_truncate() 将文件截断为最多 offset
字节的大小。
If the file previously was larger than this size, the extra data is lost. If the file previously was shorter, it is unspecified whether the file is left unchanged or is extended. In the latter case the extended part reads as zero bytes.
成功时返回 true， 或者在失败时返回 false。
注意: 此函数未在 Windows 平台下实现。