Beneath Q_OBJECT and signals/slots

The Qt building system should be clearer now. Still, the Q_OBJECT macro and the signal/slot/emit keywords are still black boxes. Let's dive into Q_OBJECT. You can Ctrl + click on the macro name, or select it and press F2 to go to its declaration.

The truth lies in the source code; Q_OBJECT is defined in the qobjectdefs.h file (in Qt 5.7):

#define Q_OBJECT \ 
public: \ 
    // skipped details 
    static const QMetaObject staticMetaObject; \ 
    virtual const QMetaObject *metaObject() const; \ 
    virtual void *qt_metacast(const char *); \ 
    virtual int qt_metacall(QMetaObject::Call, int, void **); \ 
    QT_TR_FUNCTIONS \ 
private: \ 
    // skipped details  
qt_static_metacall(QObject *, QMetaObject::Call, int, void **); 

This macro defines some static functions and static QMetaObject. The body of these static functions is implemented in the generated moc file. We will not drown you in the gory details of the QMetaObject class. The role of this class...