Class: QIODevice, QFileDevice, QFile, QTemporaryFile,……
QFile的用法：
QFile myFile = QFile("filename")
myFile.open(OpenMode mode)
这里OpenMode是一个枚举类型，只能是一下几种类型：
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Certain flags, such as Unbuffered and Truncate, are meaningless when used with some subclasses. Some of these restrictions are implied by the type of device that is represented by a subclass. In other cases, the restriction may be due to the implementation, or may be imposed by the underlying platform; for example, QTcpSocket does not support Unbuffered mode, and limitations in the native API prevent QFile from supporting Unbuffered on Windows.
The OpenMode type is a typedef for QFlags <OpenModeFlag>. It stores an OR combination of OpenModeFlag values.
可以通过用|来连接两个不同的值如：
myFile.open( QIODevice.ReadOnly | QIODevice.Text )
类似于不同位上的开关同时打开
OpenMode类型是抽象模板QFlags的一种定义
open函数若打开文件成功会返回True否则返回False
但如果打开开关Write， 那么当文件不存在是会新建一个空白文件
QFile的其他用法
