Files are a specialization of a generalized notion—that of a byte stream that resides somewhere else. Qt encapsulates the more generalized notion of byte streams in its QIODevice class, which is the parent class for QFile as well as network I/O classes such as QTcpSocket. We don't directly create a QIODevice instance, of course, but instead create a subclass such as QFile and then work with the QFile instance directly to read from and write to the file.

To begin working with a file, we first must open it using the open method. The open method takes a single argument, the manner in which the file should be opened, a bitwise combination of the following: