QTextStream has QString readLine() as well as readLineInto(QString*, qint64 max), QIODevice only has QByteArray readLine() and lacks readLineInto(QByteArray*, qint64 max).

The idea behind the -Into-functions is to preserve capacity in the string/byte-array from one line to the next, a la std::getline, unlike readLine(), which allocates a new buffer for each line.