[vdr] Coding question

Hi Mailingliste,

i have here a question about coding.

Klaus uses abstract (virtual) classes, but why is he also using the virtual keyword in this way:

class cDvbDevice : public cDevice {
private:
static bool Probe(const char *FileName);
         ///< Probes for existing DVB devices.
public:
static bool Initialize(void);
         ///< Initializes the DVB devices.
         ///< Must be called before accessing any DVB functions.
         ///< \return True if any devices are available.
private:
fe_type_t frontendType;
int fd_osd, fd_audio, fd_video, fd_dvr, fd_stc;
protected:
virtual void MakePrimaryDevice(bool On);
public:
cDvbDevice(int n);
virtual ~cDvbDevice();
virtual int ProvidesCa(const cChannel *Channel) const;
virtual bool HasDecoder(void) const;

// SPU facilities

private:
cDvbSpuDecoder *spuDecoder;
public:
virtual cSpuDecoder *GetSpuDecoder(void);

// Channel facilities

private:
cDvbTuner *dvbTuner;
void TurnOffLiveMode(void);
public:
virtual bool ProvidesSource(int Source) const;
virtual bool ProvidesTransponder(const cChannel *Channel) const;
virtual bool ProvidesChannel(const cChannel *Channel, int Priority = -1, bool *NeedsDetachReceivers = NULL) const;
protected:
virtual bool SetChannelDevice(const cChannel *Channel, bool LiveView);
public:
virtual bool HasLock(void);

I always thought that i only need to use virtual on the motherclass and the childclass dont need it.

In my biggest project, a game engine, i dont use virtual in the childclass.

Could somebody explain this to me?

Thanks, Christian