Question

该法典有:

#include <iostream>

class Outer{
    int a; // private data member of class Outer
public:
    Outer(): a(55){}
    class Inner{
    public:
        void fun(Outer ob){
            std::cout << ob.a << std::endl;
        }
    };
};

int main() {

    Outer::Inner object;
    object.fun(Outer()); // prints 55
    //std::cout << (Outer().a) << std::endl; error:  int Outer::a  is private

    return 0;
}

Why Inner class has access to private member data a of class Outer? Following this article XL C/C++ V8.0 for Linux, it should not compile, however it compiles on g++ 4.4.0.

Answer 1

根据该文件第XL C/C++号。 V8.0不支持C++11,见“Language标准合规”一节。

汇编者支持C和C++的以下方案拟订语言规格:

ISO/IEC 9899:1999 (C99)

ISO/IEC 9899:1990 (referred to as C89)

ISO/IEC 14882:2003 (referred to as Standard C++)

ISO/IEC 14882:1998, the first official specification of the language (referred to as C++98)

现行标准(ISO/IEC 14882:2011 11.7):

A nested class is a member and as such has the same access rights as any other member. The members of an enclosing class have no special access to members of a nested class; the usual access rules (Clause 11) shall be obeyed.

在以前的语文标准中,是否允许这种接触,或者至少不清楚是否应当允许这种接触,这取决于你们的解释。

Answer 2

C++03 Standard 1.1.8/1: [}.access.nest]

www.un.org/Depts/DGACM/index_spanish.htm 免职人员不能特别接触穿戴“ 封闭式班子的成员不能特别接触某类成员;通常的准入规则(clause 11)应服从。

但这是一个缺陷:

http://www. open-std.org/jtc1/sc22/wg21/docs/cwg_defects.htmlp45”rel=“nofollow”>45. 无障碍上门 >>>

在C++11中,已经纠正了这一情况:在C++11中,加固的班级确实能够接触到封闭式班级的私人成员(尽管封闭式班级仍然无法接触到被nes门班的私人成员)。

C++11 标准11.7 Nest类:

A nested class is a member and as such has the same access rights as any other member. The members of an enclosing class have no special access to members of a nested class; the usual access rules (Clause 11) shall be obeyed. [

class E {
  int x;
  class B { };
  class I {
    B b; // OK:E::I can accessE::B
    int y;
    void f(E* p, int i) {
      p->x = i; // OK:E::I can accessE::x
    }
  };
  int g(I* p) {
    return p->y; // error:I::y is private
  }
};
—end example]

The example is similar to the one you have in question and it clearly shows its valid behavior.

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