Описание тега qtextstream
The QTextStream class provides a convenient interface for reading and writing text.
QTextStream can operate on a QIODevice, a QByteArray or a QString. Using QTextStream's streaming operators, you can conveniently read and write words, lines and numbers. For generating text, QTextStream supports formatting options for field padding and alignment, and formatting of numbers.
The official Qt documentation can be found here for Qt 4.8 and here for Qt 5.