一、IO设备操作介绍
The QIODevice class is the base interface class of all I/O devices in Qt.QIODevice provides both a common implementation and an abstract interface for devices that support reading and writing of blocks of data, such as QFile, QBuffer and QTcpSocket. QIODevice is abstract and can not be instantiated, but it is common to use the interface it defines to provide device-independent l/O features.
QIODevice类是Qt中所有I/O设备的基接口类。QIODevice为支持读写数据块的设备提供了通用实现和抽象接口，例如QFile、QBuffer和QTcpSocket。QIODevice是抽象的，不能实例化，但通常使用它定义的接口来提供与设备无关的I/O功能。
二、QFile操作文件
