[英]How a friend class can access a private member of a nested class?
Consider the following example: 考虑以下示例:
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;
}
It won't compile, because the BusInfo struct is private. 它不会编译,因为BusInfo结构是私有的。 Friend classes can't access private members of nested classes by default.
默认情况下,朋友类无法访问嵌套类的私有成员。 What should I do in that situation?
在那种情况下我该怎么办? Is there any workaround?
有什么解决方法吗?
You could add a stop-printing function to SIP
: 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;
}
or you could just add operators all the way down: 或者您可以一直添加运算符:
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;
}
or any combination of approaches that suits your code. 或适合您代码的方法的任意组合。
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