Question

所以我使用Visual Studio 2008进行了以下安排：

class Base {
protected:
  int data_;
protected:
  enum {special_sauce = 1234};
};

class Derived : public Base {
  friend class DataAccessor;
};

class DataAccessor {
public:
  int AccessData(Derived* object){
    return object->data_;
  }
  bool CheckData(Derived* object){
    return object->data_ == Derived::special_sauce;
  }
};

一切运作良好。现在，进行此更改（使基础和派生（编辑：替换＆＃34;子类＆＃34;） DataAccessor的内部类...）

class DataAccessor {
public:
  class Base {
  protected:
    int data_;
  protected:
    enum {special_sauce = 1234};
  };

  class Derived : public Base {
    friend class DataAccessor;
  };

public:
  int AccessData(Derived* object){
    return object->data_;
  }
  bool CheckData(Derived* object){
    return object->data_ == Derived::special_sauce;
  }
};

我收到以下错误：

error C2248: 'special_sauce' : cannot access protected enumerator declared in class 'DataAccessor::Base'
see declaration of 'special_sauce'
see declaration of 'DataAccessor::Base'

为什么会发生这种情况，为什么会员data_不会以同样的方式受到影响？

Answer 1

对于VS编译器，听起来类似于this bug report。更多讨论here。

class BaseClass{
public :
  friend class FriendOfBaseClass;

protected :
  static void f() {};
  class InnerBaseClass {}; 
  enum TheType { state_0=0 };
};

class FriendOfBaseClass {};


class Class2 {
public :

  class InnerClassOfClass2 : public BaseClass {
  public :
    friend class FrienOfInnerClass;
  };
};


class FrienOfInnerClass : public FriendOfBaseClass {
public :
  void TheProblemIsHere()
  {    
    Class2::InnerClassOfClass2::f();                        // This compiles well
    Class2::InnerClassOfClass2::InnerBaseClass y;  // This compiles well
    int x=Class2::InnerClassOfClass2::state_0;       // Compilation error here!
  }
};

错误C2248：'state_0'：无法访问类'BaseClass'中声明的受保护枚举器

为什么不继承基类枚举？

1 个答案: