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I know there are a couple of similar questions(circular include) out stackoverflow and other websites. But I still can't figure it out and no solutions pop out. So I would like to post my specific one. I have a Event class who has 2 and actually more subclass, which are Arrival and Landing. The compiler(g++) complains: g++ -c -Wall -g -DDEBUG Event.cpp -o Event.o In file included from Event.h:15, from Event.cpp:8: Landing.h:13: error: expected class-name before ‘{’ token make: *** [Event.o] Error 1 People said that it's a circular include. The 3 header files(Event.h Arrival.h Landing.h) are as follows: the Event.h: #ifndef EVENT_H_ #define EVENT_H_ #include "common.h" #include "Item.h" #include "Flight.h" #include "Landing.h" class Arrival; class Event : public Item { public: Event(Flight* flight, int time); virtual ~Event(); virtual void occur() = 0; virtual string extraInfo() = 0; // extra info for each concrete event // @implement int compareTo(Comparable* b); void print(); protected: /************** this is why I wanna include Landing.h *******************/ Landing* createNewLanding(Arrival* arrival); // return a Landing obj based on arrival's info private: Flight* flight; int time; // when this event occurs }; #endif /* EVENT_H_ */ Arrival.h: #ifndef ARRIVAL_H_ #define ARRIVAL_H_ #include "Event.h" class Arrival: public Event { public: Arrival(Flight* flight, int time); virtual ~Arrival(); void occur(); string extraInfo(); }; #endif /* ARRIVAL_H_ */ Landing.h #ifndef LANDING_H_ #define LANDING_H_ #include "Event.h" class Landing: public Event {/************** g++ complains here ****************/ public: static const int PERMISSION_TIME; Landing(Flight* flight, int time); virtual ~Landing(); void occur(); string ex

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