无法访问类“std::basic_ios<_Elem,_Traits>”中声明的私有成员

此特定方法有问题，不知道如何解决！我收到的错误是上面的：

“错误 C2248：'std::basic_ios<_elem>::basic_ios'：不能 访问类中声明的私有成员 'std::basic_ios<_elem>' C:\Program Files\Microsoft Visual Studio 10.0\VC\include\ostream 604"

我的方法是：

ostream operator<<( ostream & stream, ProcessClass const & rhs )
{
  stream << rhs.name_;
  return stream;
}

并在标题中：

friend std::ostream operator<<( std::ostream & stream, ProcessClass const & rhs );

关于如何解决这个问题有什么想法吗？我认为这与通过引用传递而不是值有关......但我有点困惑！

返回类型应该是ostream &这是一个参考ostream.

ostream & operator<<( ostream & stream, ProcessClass const & rhs )
{    //^^^ note this!
  stream << rhs.name_;
  return stream;
}

When you return by value (instead of reference), then that requires copying of stream object, but copying of any stream object in C++ has been disabled by having made the copy-constructor¹ private.

^{1. and copy-assignment as well.}

要知道为什么要复制any流已被禁用，请在此处阅读我的详细答案：

• 为什么不允许复制字符串流？ https://stackoverflow.com/questions/6010864/why-copying-stringstream-is-not-allowed/6010930#6010930