朋友班級如何訪問嵌套班級的私有成員？

Question

考慮以下示例：

class SIP{
    public:
        friend std::ostream& operator<<(std::ostream& os, const SIP& c);
    private:
        class BusStop;
        std::vector<BusStop*> mbusStops;
};

class SIP::BusStop{
    private:
        struct BusInfo;
        std::vector<BusInfo*> mbusStopTerminal;
};

struct SIP::BusStop::BusInfo{
    std::string from;
    std::string to;
};

std::ostream& operator<<(std::ostream &os, const SIP &c) {
    for (std::vector<SIP::BusStop*>::const_iterator it = c.mbusStops.begin(); 
         it != c.mbusStops.end(); it++){
        for (std::vector<SIP::BusStop::BusInfo*>::const_iterator it2 = mbusStopTerminal.begin(); 
             it2 != mbusStopTerminal.end(); it2++){
        }
    }
    return os;
}

它不會編譯，因為BusInfo結構是私有的。 默認情況下，朋友類無法訪問嵌套類的私有成員。 在那種情況下我該怎么辦？ 有什么解決方法嗎？

Answer 1

您可以在SIP添加停止打印功能：

class SIP{
    public:
        friend std::ostream& operator<<(std::ostream& os, const SIP& c);
    private:
        void printStops(std::ostream& os);
        class BusStop;
        std::vector<BusStop*> mbusStops;
};

std::ostream& operator<<(std::ostream &os, const SIP &c) {
    c.printStops(os);
    return os;
}

或者您可以一直添加運算符：

class SIP{
    public:
        friend std::ostream& operator<<(std::ostream& os, const SIP& c);
    private:
        class BusStop;
        std::vector<BusStop*> mbusStops;
};

class SIP::BusStop{
    private:
        friend std::ostream& operator<<(std::ostream& os, const BusStop& c);

        struct BusInfo;
        std::vector<BusInfo*> mbusStopTerminal;
};

struct SIP::BusStop::BusInfo{
    std::string from;
    std::string to;
};

std::ostream& operator<<(std::ostream &os, const SIP::BusStop::BusInfo &i)
{
   // Whatever
}

std::ostream& operator<<(std::ostream &os, const SIP::BusStop &c)
{
    for (std::vector<SIP::BusStop::BusInfo*>::const_iterator it = mbusStopTerminal.begin(); 
         it != mbusStopTerminal.end(); it++){
        os << **it;
    }   
}

std::ostream& operator<<(std::ostream &os, const SIP &c) {
    for (std::vector<SIP::BusStop*>::const_iterator it = c.mbusStops.begin(); 
         it != c.mbusStops.end(); it++){
        os << **it;
    }
    return os;
}

或適合您代碼的方法的任意組合。