C++ Doubly Linked List with Pointers: Object of class isn't constructed properly

C++ Doubly Linked List with Pointers: Object of class isn't constructed properly

By : Aarzoo Varshney
Date : November 27 2020, 01:01 AM
wish of those help I think what I'd start with is your print function, which doesn't deal well with the case where the list is empty. Here I've made sure not to use the pointer current when it's null. We can be sure that it's safe to use it within the while loop scope because I've constrained it to current != nullptr
code :
void linked_list::print() {
    Node* current = head;
    cout << "[";
    bool bFirst = true;
    while (current != nullptr) {  // was current->next
        if (bFirst) {
            bFirst = false;
        } else {
            cout << ", ";
        cout << current->value;
        current = current->next;
    cout << "]" << endl; //no longer referencing current->value here where it's unsafe
void linked_list::append(int value) {
    if(head == nullptr && tail == nullptr) {
        head = new Node(value);
        tail = head;
    } else { 
        tail->next = new Node(value);
        tail->next->previous = tail;
        tail = tail->next;
void linked_list::remove(int index) {
    Node* current = head;
    for (int i = 0; (i < index) && (current != null) ; i++) {
        current = current->next;
    if (current != null) {
        Node* next = current->next;
        Node* previous = current->previous;

        if (next == null) {
            tail = previous; // no next
        } else {
            next->previous = previous;

        if (previous == null) {
            head = next; //no previous
        } else {
            previous->next = next;
        size --; //only if we found something

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Comparing pointers within a doubly linked list?

Comparing pointers within a doubly linked list?

By : R.Daria
Date : March 29 2020, 07:55 AM
around this issue I am trying to build a simple text adventure for finals week. It's pretty standard stuff. Use 'n', 'e', 's', and 'w' to traverse the house, and try to get to the end of the maze. All was going well for a while, but I'm running into a problem when I try to retrieve a list of available doors. , This code
code :
for(int i=0; i<allDoorsLen; i++)
    if(allDoors[i] != NULL)
    //filters out any NULL pointers and keeps track of the # of non-NULL pointers
        availableDoors[i] = allDoors[i];
availableDoors[i] = allDoors[i]
availableDoors[availableDoorsLen] = allDoors[i]
Vector of Doubly Linked Lists of Doubly Linked List Pointers

Vector of Doubly Linked Lists of Doubly Linked List Pointers

By : rinaus
Date : March 29 2020, 07:55 AM
wish helps you In addition to the issue you described, the other problem with storing your structures directly in a vector is that certain operations on a vector invalidate some or all existing pointers to the vector. Namely removing from, or inserting elements into the vector.
Generally, in situations like these, it's better for the vector to store pointers to objects, rather than the objects themselves. In your example, a std::vector< DoublyLinkedList *> is going to work better. Your various instances of DoubleLinkedList can store pointers to each other, directly, and moving the pointers around in the vector won't have any effect on their validity.
Initialize doubly linked list in C, pointers

Initialize doubly linked list in C, pointers

By : Joseph W Britton
Date : March 29 2020, 07:55 AM
wish helps you Is it possible to initiate the value for *preceding and *next on one line of code? , You can define both links in a single line.
code :
struct entry
    int            value;
    struct entry   *preceding, *next;
int main() {

    typedef struct LinkedList {
        struct LinkedList   *prev, *next;
        int value;
    } linkedList_t;

    linkedList_t head =  { &head, &head, 0 };
Pointers and doubly-linked list

Pointers and doubly-linked list

By : S Piracha
Date : March 29 2020, 07:55 AM
Any of those help The evaluation is first done on the right side and then operator= kicks in and does the assignment. This is caused by the priority of operator=. See C++ Operator Precedence.
At the first line of main, you are creating a Link with name "Thor" and pointing norse_gods to it.
before and after pointers, doubly linked list in c++

before and after pointers, doubly linked list in c++

By : Jonathan Beaton
Date : March 29 2020, 07:55 AM
help you fix your problem With two dummy nodes, there are no special cases. Since you always have a dummy node in front and a dummy node at the end, you never operate on an empty list. You never insert at the very front. You never insert at the very back. All insertions and deletions are in the middle -- that's the point of the two sentinel nodes.
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