Search code examples
c++classpointersprivate

member "Node::next" (of a friend class) is inaccessible

I am building my own LinkedList, because I need a special Node that holds more data. I specify that my Node class is a friend of the LinkedList class, but it doesn't seem to allow me to access the private variables in the Node class from the LinkedList class.

Node.h

class Node {
    private:
        Node* next;
    ...
};

LinkedList.h

#include "Node.h"

class LinkedList {
    friend class Node;
    ...
};

LinkedList.cpp

...
void LinkedList::insertFirst(Node* n) {
    Node* temp = this->root;
    this->root = n;
    this->root->next = temp; // 1
}
...

1 This is where I get the error. It says that the this->root->next is inaccessible, but I have it as a friend class to my LinkedList and so private variables should be accessible to it.

There are quite a few questions here on Stack Overflow that talk about something similar to my question, but none of them seem to be what I need.

  • One answer was saying to switch from private to protected, but that didn't work, it just changed the error to say it can't access the protected member.
  • Another answer was saying that they had a misspelling in there friend declaration. I checked mine, and it is spelled correctly.
  • Another was saying to make sure that the classes are declared in the correct order, but since I have them in different files, and #include the file where I create the class that is declared as a friend.

There were quite a few more that I looked at, but all were similar to the above mentioned and didn't help me solve my problem.

What am I missing/not understanding? Nothing I've tried has worked, and I would really appreciate any help.

Solution

  • A friend declaration grants access of the specified class to the private members of the declaring class (ie, "that class X over there is a friend of mine, he has permission to use my private stuff").

    So, by declaring Node as a friend inside of LinkedList, you are granting Node access to LinkedList's private members, not the other way around like you want.

    To let LinkedList access Node::next, you need to declare LinkedList as a friend of Node instead:

    class Node {
    friend class LinkedList;
    ...
};