我不明白这一行 - 解除引用一个私有成员变量的地址或什么？ [英] I can't understand this line - dereferencing an address of private member variable or what?

问题描述

我以前问过一个问题关于访问STL适配器的底层容器。我得到了非常有帮助的答案：

 模板< class T，S类，C类> 
 S& container（priority_queue< T，S，C>& q）{
 struct HackedQueue：private priority_queue< T，S，C& {
 static S& Container（priority_queue< T，S，C>& q）{
 return q。*& HackedQueue :: c; 
} 
}; 
 return HackedQueue :: Container（q）; 
} 
 
 int main（）
 {
 priority_queue< SomeClass> pq; 
 vector< SomeClass> & tasks = Container（pq）; 
 return 0;不幸的是，我不明白这一行：
 
 
 
 
 
 
 $ b 
  return q。*& HackedQueue :: c; 
  
这行代码是什么？此外，该行如何访问传递给函数 Container ？
的 priority_queue  
 
解决方案
想像这样：
 （q）。*（& HackedQueue :: c）; 
  
首先，你有HackedQueue :: c，它只是一个成员变量的名字。然后你取& HackedQueue :: c，它是一个指向那个成员变量的指针。接下来你取 q ，这只是一个对象引用。然后你使用绑定指针到成员引用操作符。* 使用 q 作为 。
 
 
 
至于私人成员问题， priority_queue :: c 只受保护，不是私人的，所以当你从 priority_queue 派生时，你可以访问其受保护的成员。
 
I asked a question while ago about accessing the underlying container of STL adapters. I got a very helpful answer:
template <class T, class S, class C>
    S& Container(priority_queue<T, S, C>& q) {
        struct HackedQueue : private priority_queue<T, S, C> {
            static S& Container(priority_queue<T, S, C>& q) {
                return q.*&HackedQueue::c;
            }
        };
    return HackedQueue::Container(q);
}

int main()
{
    priority_queue<SomeClass> pq;
    vector<SomeClass> &tasks = Container(pq);
    return 0;
}
Unfortunately, I couldn't understand this line:
return q.*&HackedQueue::c;
What does this line do? Also, how could that line access the private container in priority_queue that is passed to the function Container?
解决方案
Think of it like this:
(q).*(&HackedQueue::c);
First, you have HackedQueue::c, which is just the name of a member variable.  Then you take &HackedQueue::c, which is a pointer to that member variable.  Next you take q, which is just an object reference.  Then you use the "bind pointer to member by reference" operator .* to bind the member variable referred to by the member-variable pointer using q as the this.

As to the private member issue, priority_queue::c is only protected, not private, so it should come as no surprise that when you derive from priority_queue, that you can access its protected members.

                        
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