C++ cyclic inclusion issue [duplicate]

Answer 1

When you forward declare, don't put in the #include. Do it like

class Event;
class Logger {
public:
    /*!
     * Constructor
     */
    Logger();
    /*!
     * Destructor
     */
    ~Logger();
    /*!
     * My operator
     */
    Logger& operator<<(const Event& e);
private:
    ...
};

without the #include "event.hpp"