Question

struct TimerEvent {    event Event;    timeval TimeOut;    static void HandleTimer(int Fd, short Event, void *Arg); }; 

HandleTimer needs to be static since I’m passing it to C library (libevent).

I want to inherit from this class. How can this be done?

Thanks.

Answer 1

You can easily inherit from that class:

class Derived: public TimerEvent {     ... }; 

However, you can’t override HandleTimer in your subclass and expect this to work:

TimerEvent *e = new Derived(); e->HandleTimer(); 

This is because static methods don’t have an entry in the vtable, and can’t thus be virtual. You can however use the ‘void* Arg’ to pass a pointer to your instance… something like:

struct TimerEvent {     virtual void handle(int fd, short event) = 0;      static void HandleTimer(int fd, short event, void *arg) {         ((TimerEvent *) arg)->handle(fd, event);     } };  class Derived: public TimerEvent {     virtual void handle(int fd, short event) {         // whatever     } }; 

This way, HandleTimer can still be used from C functions, just make sure to always pass the ‘real’ object as the ‘void* Arg’.