Description
bool 
dio_truncate ( resource fd, int offset)
     Function dio_truncate() causes the file
     referenced by fd to be truncated to at
     most offset bytes in size.  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. 如果成功则返回 TRUE,失败则返回 FALSE。.