accessing struct members using pointer to pointer

Question

I have a program like below, when I try to access a struct member using pointer to pointer it says the expression must have a pointer to class type. Please tell me how can I access data element of the struct object using a pointer to pointer

#include "stdafx.h"
#include<iostream>
struct Node{
    int data;
    Node* next;
};

void addnode(Node** node, int val)
{
    if (node == NULL){
        *node = new Node();
        *node->data = val;

    }
}



int _tmain(int argc, _TCHAR* argv[])
{
    Node* node;
    addnode(&node, 10);
    return 0;
}

Answer 1

In *node->data = val; there are 3 operators involved.

• operator* to dereference
• operator-> to access a member
• operator= to do the assignment

In which order will these happen? According to operator precedence which states:

Precedence	Operator
2	operator->
3	operator*
16	operator=

node->data will happen first and then the result will be dereferenced - so you have *(node->data) on the left hand side.

You need to dereference node first and can use (... ) to override the precedence rules:

(*node)->data = val;

Also note that your original Node* is uninitialized and reading it (like you do in if(node == NULL) ) will cause the program to have undefined behavior. Initialize it to nullptr:

Node* node = nullptr; // here
addnode(&node, 10);