c++ - How to fix: Exception thrown: write access violation. list.tail was 0xCCCCCCCC

Question

I am using struct to create a node and a linked list. But I got an error about the tail of the linked list and I don't know why. The purpose of the task is to load the data in the "items.txt" into the linked list I created. But it seems that the error occurs in the tail of the linked list. But I don't know how to fix this.

#include <iostream>
#include <fstream>
#include <string>

using namespace std;

struct item
{
    string itemId, title, type, loan, copy, fee, genre;
};

typedef struct item Item;

struct node
{
    Item data;
    node* next;
};

typedef struct node Node;

struct linkedList
{
    Node* head;
    Node* tail;
};

typedef struct linkedList list;

void createList(list& list)
{
    list.head = NULL;
    list.tail = NULL;
}

Node* createNode(item newData)
{
    Node* point = new Node;
    if (point == NULL)
    {
        cout << "Failed." << endl;
        return NULL;
    }
    point->data = newData;
    point->next = NULL;
    return point;
}

void insertHead(list& list, Node* point)
{
    if (list.head == NULL)
    {
        list.head = list.tail = point;
    }
    else
    {
        point->next = list.head;
        list.head = point;
    }
}
void appenTail(list& list, Node* point)
{
    if (list.head == NULL)
    {
        list.head = point;
        list.tail = point;
    }
    else
    {
        list.tail->next = point;
        list.tail = point;
    }
}

void readFirstLine(ifstream& file, Item& item)
{
    getline(file, item.itemId, ',');
    getline(file, item.title, ',');
    getline(file, item.loan, ',');
    getline(file, item.copy, ',');
    getline(file, item.fee, ',');
    getline(file, item.genre, '
');
}

void readAllFile(ifstream& file, list& list)
{
    while (!file.eof())
    {
        Item item;
        readFirstLine(file, item);
        Node* point = createNode(item);
        appenTail(list, point);
    }
}

void printLine(item item)
{
    cout << item.itemId << endl;
    cout << item.title << endl;
    cout << item.loan << endl;
    cout << item.copy << endl;
    cout << item.fee << endl;
    cout << item.genre << endl;
}
   
void printAll(list list)
{
    int count = 1;
    for (Node* point = list.head; point != NULL; point = point->next)
    {
        cout << "Item number " << count;
        printLine(point->data);
    }
}

int main(int argc, char* argv[])
{
    Item item;
    list list;
    ifstream file("items.txt", ios::in);
    string line;
    if (!file)
    {
        cerr << "Error in opening file.";
        exit(EXIT_FAILURE);
    }
    readAllFile(file, list);
    printAll(list);
    file.close();
    return 0;
}

The problem i got is in the line 70.

Thanks in advance.

Answer 1

Your list is uninitialized when it's declared. Hence, it's head and tail members point to garbage instead of NULL.

Your forgot to call your own createList function. You could do that. Or...

Change this:

int main(int argc, char* argv[])
{
    Item item;
    list list;

To be this:

int main(int argc, char* argv[])
{
    Item item;
    list list = {};  // this will set head and tail to NULL