c++ - 如何与私有(private)嵌套类成为 friend

Question

我认为我可以这样做:

class TestA
{
private:
  class Nested
  {

  };
};

class TestB
{
public:
  friend class TestA;
  friend class TestA::Nested;
};

但我得到一个错误:

Error C2248 'TestA::Nested': cannot access private class declared in class

有没有办法让私有(private)嵌套类成为 friend ？我该怎么做？

我在尝试在 MSVC 2017 (C++17) 中编译 MSVC 6 项目时遇到此错误。我想它当时有效。

Answer 1

与您访问任何其他私有(private)事物的方式相同。你需要另一种友元:

class TestA
{
  friend class TestB; // <== this
private:
  class Nested
  {

  };
};

class TestB
{
public:
  friend class TestA;
  friend class TestA::Nested; // <== now we're a friend of TestA, so we can access it
};