C++:从外部在类内声明枚举器，因此可以在私有(private)成员中使用

Question

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Answer 1

您不能在类外声明嵌套枚举。您还必须在使用它之前对其进行定义。

class Printer {                  // choose one of monitor or cormonitor
  public:
    enum States { Starting = 'S', Blocked = 'B', Unblocked = 'U', Finished = 'F', // general
      Napping = 'N', Awake = 'A',             // Santa
      Working = 'W', NeedHelp = 'H',          // elf
      OnVacation = 'V', CheckingIn = 'I',     // reindeer
      DeliveringToys = 'D', DoneDelivering = 'd', // Santa, reindeer
      Consulting = 'C', DoneConsulting = 'c' // Santa, elves
    };
  private:
    States taskStates[];
  public:
    Printer();
    void print( unsigned int id, States state );
    void print( unsigned int id, States state, unsigned int numBlocked );
};

作为旁注，C++11 的 enum class 只需在类内声明 - 它可以在类外定义。