error expected class-name before token

Question

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 extraInfo         endif    LANDING H       UPDATE   I included Landing h due to Landing s constructor is called in the Event  createNewLanding method   Landing  Event  createNewLanding Arrival  arrival        return new Landing flight  time   Landing  PERMISSION TIME

User · Answer

This should be a comment  but comments don t allow multi-line code   Here s what s happening   in Event cpp   include  Event h    preprocessor starts processing Event h   ifndef EVENT H    it isn t defined yet  so keep going   define EVENT H   include  common h    common h gets processed ok   include  Item h    Item h gets processed ok   include  Flight h    Flight h gets processed ok   include  Landing h    preprocessor starts processing Landing h   ifndef LANDING H    not defined yet  keep going   define LANDING H    include  Event h    preprocessor starts processing Event h   ifndef EVENT H    This IS defined already  the whole rest of the file gets skipped   Continuing with Landing h  class Landing  public Event     The preprocessor doesn t care about this  but the compiler goes  WTH is Event   I haven t heard about Event yet

User · Answer

I know it is a bit late to answer this question  but it is the first entry in google  so I think it is worth to answer it   The problem is not a coding problem  it is an architecture problem   You have created an interface class Event  public Item to define the methods which all events should implement  Then you have defined two types of events which inherits from class Event  public Item  Arrival and Landing and then  you have added a method Landing  createNewLanding Arrival  arrival   from the landing functionality in the class Event  public Item interface  You should move this method to the class Landing  public Event class because it only has sense for a landing  class Landing  public Event and class Arrival  public Event class should know class Event  public Item but event should not know class Landing  public Event nor class Arrival  public Event   I hope this helps  regards  Alberto

User · Answer

If you forward-declare Flight and Landing in Event h  then you should be fixed   Remember to  include  Flight h  and  include  Landing h  in your implementation file for Event   The general rule of thumb is   if you derive from it  or compose from it  or use it by value  the compiler must know its full definition at the time of declaration   If you compose from a pointer-to-it  the compiler will know how big a pointer is   Similarly  if you pass a reference to it  the compiler will know how big the reference is  too

User · Answer

I got the same error with a different problem   I used namespaces in my headers and forgot the closing bracket and got this cryptic error instead

User · Answer

Replace   include  Landing h    with  class Landing    If you still get errors  also post Item h  Flight h and common h  EDIT  In response to comment   You will need to e g   include  Landing h  from Event cpp in order to actually use the class  You just cannot include it from Event h

[c++] error: expected class-name before ‘{’ token

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