使用类的C ++链接列表（OOP）

Question

This is my first post on StackOverflow, as I am genuinely stuck. My issue is that everytime I run the following code, at the first call for the function InsertNode(), the return temp node has the correct values for next node and data. However, when the function is called again, for some reasons the head gets reset to data NULL and next pointer recursively pointing to the same address. I'm having a hard time implementing this in OOP, I have done this using plain structs successfully. But with OOP I'm confused as how to declare the Node* Node::InsertNode(Node* head), method in main, as I get an error that InsertNode is undeclared. So as workaround I declared InsertNode outside of the Node class as an independent function. I have a feeling that is what may be causing the issue. would appreciate some help on what is going on or what I should change in my code. Thank you!

hashtable.cpp

#include "Hashtable.hpp"
using namespace std; 
Node::Node(){

    data = NULL;
   Node* nextP = NULL;
};

Node::~Node(){

}

Node* InsertNode(Node* head, int data){

    Node* temp = new Node();

    if(head->nextP == NULL){

        head->data = data;
        temp->nextP = head;
        head = temp;

    } else if(head->nextP!=NULL){

        temp->nextP = head;
        temp->data = data;
        head = temp;
    }

    return head;
};

void Node::printNode(Node* head){
    Node* temp = new Node();
    temp = head;
    while(temp->nextP != NULL){
        printf("%d\n", temp->data);
        temp = temp->nextP;
    }
}

Hashtable.hpp

#ifndef Hashtable_hpp
#define Hashtable_hpp

#include <stdio.h>

class Node
{
public:
    Node* nextP;
    Node();
    ~Node();

    void printNode(Node* head);
    int data = NULL;

    private:


};
Node* InsertNode(Node* head, int data);

#endif /* Hashtable_hpp */

main.cpp

#include <iostream>
#include "stdio.h"
#include <string>
#include "Hashtable.hpp"

using namespace std;
Node head;
//Node* head = new Node();


int main(int argc, const char * argv[]) {
    // insert code here...
    std::cout << "Hello, World!\n";
   head =  *InsertNode (&head, 10);
   // head = temp2;
   head =  *InsertNode (&head, 20);
   // head = temp2;
   head =  *InsertNode (&head, 30);
   // head = temp2;

     //InsertNode(head, 20);

  Node printNode(head);

    return 0;


}

Answer 1

So I finally figured out the issue. Since initially I was referencing the class function InsertNode() directly, I was trying avoid the error that I was other getting with the undeclared identifier. So as a work around I moved the function outside of the class declaration, which then caused more problems as you saw above post. Now I realized that when the function exists inside the Class, I have reference it by first de-referencing (my terminology is probably wrong) the function using the following: head->InsertNode(head, data); I was initially trying different iterations of InsertNode(&head, data) or Node* InsertNode(&head, data) ... etc. Basically trying to brute force my way through the compiler :).

I am attaching the code below, please let me know your comments on what I can improve.

Hashtable.cpp

#include "Hashtable.hpp"
#include <iostream>

using namespace std;

Node::Node(){

    data = NULL;
    Node* nextP = NULL;
};

Node::~Node(){

}

Node* Node::InsertNode(Node* head, int data){
    Node* temp = new Node();
    if(head->nextP == NULL){
        head->data = data;
        temp->nextP = head;

    } else if(head->nextP!=NULL){
        temp->nextP = head;
        temp->data = data;
    }

    return temp;
};


void Node::printNode(Node* head){
    Node* temp = new Node();
    temp = head;
    while(temp->nextP != NULL){
        printf("%d\n", temp->data);
        temp = temp->nextP;
    }
}

Hashtable.hpp

#ifndef Hashtable_hpp
#define Hashtable_hpp

#include <stdio.h>
#include <iostream>

using namespace std;

class Node
{
    int data = NULL;
    Node* nextP;
public:

    Node();
    ~Node();
    Node* InsertNode(Node* head, int data);
    void printNode(Node* head);
        private:
};


#endif /* Hashtable_hpp */

main.cpp

#include <iostream>
#include "stdio.h"
#include <string>
#include "Hashtable.hpp"

using namespace std;
Node* head = new Node();

int main(int argc, const char * argv[]) {
    // insert code here...
    std::cout << "Hello, World!\n";
    Node temp2;
    head =  head->InsertNode (head, 10);
    head =  head->InsertNode (head, 20);
    head =  head->InsertNode (head, 30);
    head =  head->InsertNode (head, 40);
    head =  head->InsertNode (head, 50);
    head =  head->InsertNode (head, 60);
    head =  head->InsertNode (head, 70);
     head->printNode(head);

    return 0;