嵌套类访问封闭类的私有数据成员(Nested class' access to enclosing class' private data members)

 我在实现一个嵌套类的时候遇到了麻烦，它的构造函数是用一些封闭类的私有数据成员初始化的。 
 
 例： 
 
Header File:
class Enclosing {
   //...Public members
   //...Private members
   int x, int y
   class Inner; // Declaration for nested class
};

Impl. File:
// Stuff...
class Enclosing::Inner {
    explicit Inner() : foo(x), bar(y) // foo and bar are data members of Inner
    //...
};
 
 我得到了invalid use of non-static data member错误的invalid use of non-static data member 。 当涉及到嵌套类访问其封闭类的成员时，是否有某些我错过了？ 

I'm having trouble implementing a nested class who's constructor is initialized with some of the enclosing class' private data members.
 
Example:
 
Header File:
class Enclosing {
   //...Public members
   //...Private members
   int x, int y
   class Inner; // Declaration for nested class
};

Impl. File:
// Stuff...
class Enclosing::Inner {
    explicit Inner() : foo(x), bar(y) // foo and bar are data members of Inner
    //...
};
 
I get an invalid use of non-static data member error. Is there something I'm missing when it comes to nested class access to its enclosing class' members?

原文：https://stackoverflow.com/questions/1604853