Files are basically digital information stored in the form of byte stream that reside somewhere in your hard disk. If your program needs to save or load data, such as for word processing, image editing, media streaming, or program configuration, you will need to access the files stored on your local hard drive. Qt provides us with classes that allow us to easily access the filesystem regardless of the type of operating system.
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 something such as a QFile subclass and then work with the QFile instance directly to read from and write to the file.