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.
Tip
Files and network access usually take time, and thus, your applications shouldn't work with them on the main thread. Consider creating a subclass of QThread to perform I/O operations such as reading from files or accessing the network.
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: