statement, the space between the end of the newly written record and the next record is padded with existing data from the file that you are writing to. Note for binary files:
子句里面指定数据的长度不匹配的话，那么介于新写入的数据的末尾和下一条记录之间的空间，将会用你正在写入的文件中的现有数据进行填充。