QSlider with double Heads..

[jacek]

Q_Q(QAbstractSlider) seems to give access to some member q, and likewise Q_D(QAbstractSlider) makes some member d available

what do these macros mean?

#define Q_D(Class) Class##Private * const d = d_func()
#define Q_Q(Class) Class * const q = q_func()

#define Q_D(Class) Class##Private * const d = d_func()
#define Q_Q(Class) Class * const q = q_func()

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Q_D macro declares a variable that points to the private part of the implementation, while Q_Q works the other way around --- gives you access to public part of the implementation.

If you want to know why the implementation is split into public and private part, ask google about "pimpl".