Question

I feel this question may be a bit trivial, but I simply cannot wrap my head around it. I currently have a class, Node, which is trying to point to what node occurs before the current node using the pointer prevNode. However I seem unable to access any variables within prevNode.

When running Main.cpp from the following code, it prints the result ‘15340756’. Where am I going wrong? Appologies as Im still a bit new to C++.

Node.h

#include "stdafx.h"

class Node
{
public:
    Node();
    void setPrevNode(Node n);
    Node getPrevNode();
    int i;
private:
    Node *prevNode;
};

Node.cpp

#include "stdafx.h"
#include "Node.h"

Node::Node(){
    i = 0;
}

void Node::setPrevNode(Node n){
    prevNode = &n;
}

Node Node::getPrevNode(){
    return *prevNode;
}

Main.cpp

#include "stdafx.h"
#include "Node.h"


int _tmain(int argc, _TCHAR* argv[])
{
    Node nodes[] = {Node(), Node()};

    nodes[0].i = 1;
    nodes[1].setPrevNode(nodes[0]);
    printf("%i", nodes[1].getPrevNode().i); 
    while(true){

    }
    return 0;
}

Answer 1

void setPrevNode(Node n);

Here setPrevNode is declared to take a copy of the node passed as an argument, and point to such node. After the function returns, the pointed to node no longer exist and what you get is undefined behavior.

What you want is to take the Node either as a reference or a pointer instead:

void setPrevNode(Node& n)
{
    prevNode = &n;
}

void setPrevNode(Node* n)
{
    prevNode = n;
}

On the same line, getPrevNode is defined to return a copy of the previous node. You most certainly want to return a reference here instead, although you can also return a pointer:

Node& getPrevNode()
{
    return *prevNode;
}

Node* getPrevNode()
{
    return prevNode;
}