无法访问 class (C++) 的私有成员

Question

I developed a solution in c++ that is using linked lists. First, I used struct to create my list and the nodes (which worked perfectly), but now I am required to have Data private so i am now using classes instead. I can not access the private members of my two classes.

Here is my node class

class node{                                                         //class for a node  ;
        private:
            int info;
            class node *next;
        public:
            node();
            node(int info1,node myNode){
                info1 = info;
                *next = myNode;
            }
    };
    typedef class node Node;                                        //the new class called Node

Here is my list class

    class mylist{                                                       //class for a list   ;
    private:
        Node *head;
        Node *tail;
    public:
        mylist();
        mylist(node a, node b){
        *head = a;
        *tail = b;
        }
        node getHead(){
            return *head;
        }
        node getTail(){
            return *tail;
        }
};
typedef class mylist Tlist;                                        //the new class called Tlist

Here is the function from which I am trying to access members of a class:

int isEmpty(Tlist l){
    /** Return true if the head of the list is NULL and false otherwise **/
    return getHead(l.head) == NULL;   //error occurs for this line ('Node mylist::head' is private within this content)
}

Answer 1

You are implementing the empty check as a free function. This function does not have access to the private members.

Two possible solutions:

First is free function using public members (usage: isEmpty(l) ):

bool isEmpty(Tlist l){
    /** Return true if the head of the list is NULL and false otherwise **/
    return l.getHead() == nullptr;   //error occurs for this line ('Node mylist::head' is private within this content)
}

Second is a member function (usage: l.isEmpty() ):

class mylist {
public:
    bool isEmpty(){
        /** Return true if the head of the list is NULL and false otherwise **/
        return head == nullptr;   //error occurs for this line ('Node mylist::head' is private within this content)
    }
}

Please note that I changed NULL (C style) to nullptr and the return value from int to bool . Your body of the function looked strange too, so I changed it to what seems more appropriate.