These classes are used to handle input and output to and from external devices, processes, files etc. as well as manipulating files and directories.
| QAbstractFileEngine | Abstraction for accessing the filesystem | 
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| QAbstractFileEngineHandler | Way to register custom file engines with your application | 
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| QBuffer | QIODevice interface for a QByteArray | 
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| QDataStream | Serialization of binary data to a QIODevice | 
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| QDir | Access to directory structures and their contents | 
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| QFile | Interface for reading from and writing to files | 
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| QFileInfo | System-independent file information | 
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| QFileSystemWatcher | Interface for monitoring files and directories for modifications | 
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| QIODevice | The base interface class of all I/O devices in Qt | 
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| QImageReader | Format independent interface for reading images from files or other devices | 
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| QImageWriter | Format independent interface for writing images to files or other devices | 
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| QProcess | Used to start external programs and to communicate with them | 
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| QProcessEnvironment | Holds the environment variables that can be passed to a program | 
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| QResource | Interface for reading directly from resources | 
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| QSettings | Persistent platform-independent application settings | 
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| QSocketNotifier | Support for monitoring activity on a file descriptor | 
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| QTemporaryFile | I/O device that operates on temporary files | 
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| QTextDocumentWriter | Format-independent interface for writing a QTextDocument to files or other devices | 
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| QTextStream | Convenient interface for reading and writing text | 
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| QUrl | Convenient interface for working with URLs | 
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| QUrlInfo | Stores information about URLs | 
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