Updating a node in linked list - c++

Question

I want to update a data in the node of the linked list. I have tried to but it does not changed the data within. If anyone can help me with this, i would be really appreciated.
This is my Main Driver Code
#include <iostream>
#include <fstream>
#include <string>
#include "item.h"
using namespace std;
LinkedList list;
Item item;
Node* node;
void menu()
{
here:
int choice = 0;
string itemId, title, type, loan, num_copy, fee, genre;
cout << "Welcome to Genie\'s video store" << endl;
cout << "Enter an option below" << endl;
cout << "1. Add a new item" << endl;
cout << "2. Delete an item" << endl;
cout << "3. Update an item" << endl;
cout << "4. Search an item by ID" << endl;
cout << "5. Search an item by title" << endl;
cout << "6. Display all item" << endl;
cout << "Exit" << endl;
cout << "Enter your choice: ";
cin >> choice;
if (choice == 1)
{
system("cls");
list.addItem(list);
cout << endl;
goto here;
}
else if (choice == 2)
{
system("cls");
list.deleteItem(list);
cout << endl;
goto here;
}
else if (choice == 3)
{
system("cls");
list.updateItem(list);
cout << endl;
goto here;
}
else if (choice == 4)
{
system("cls");
list.searchById(list);
cout << endl;
goto here;
}
else if (choice == 5)
{
system("cls");
list.searchByTitle(list);
cout << endl;
goto here;
}
else if (choice == 6)
{
system("cls");
list.printAll(list);
cout << endl;
goto here;
}
}
int main(int argc, char* argv[])
{
ifstream file("items.txt", ios::in);
if (!file)
{
cerr << "Error in opening file.";
throw(file);
}
list.readAllFile(file, list);
file.close();
menu();
return 0;
}
And this is my item.h:
#pragma once
#include <iostream>
#include <fstream>
#include <string>
using namespace std;
class Item
{
protected:
string itemId, title, type, loan, num_copy, fee, genre;
public:
Item() {}
Item(string itemId, string title, string type, string loan, string num_copy, string fee, string genre)
: itemId(itemId), title(title), type(type), loan(loan), num_copy(num_copy), fee(fee), genre(genre)
{}
~Item() {}
string& getItemId() { return this->itemId; }
string& getTitle() { return this->title; }
string& getType() { return this->type; }
string& getLoan() { return this->loan; }
string& getCopy() { return this->num_copy; }
string& getFee() { return this->fee; }
string& getGenre() { return this->genre; }
void setItemId(string itemId) { this->itemId = itemId; }
void setTitle(string title) { this->title = title; }
void setFee(string fee) { this->fee = fee; }
void setCopy(string num_copy) { this->num_copy = num_copy; }
void setLoan(string loan) { this->loan = loan; }
void setType(string type) { this->type = type; }
void setGenre(string genre) { this->genre = genre; }
};
class Node
{
private:
Item data;
Node* next;
public:
Node() {}
Node(Item newData)
{
data = newData;
next = nullptr;
}
Node(Item newData, Node* nextNode)
{
data = newData;
next = nextNode;
}
~Node() {}
Node* getNext() { return next; }
void setNext(Node* newNext) { next = newNext; }
Item getData() { return data; }
Item setData(Item newData) { data = newData; }
Node* createNode(Item newData);
};
class LinkedList
{
private:
Node* head;
Node* tail;
public:
LinkedList() : head(NULL), tail(NULL)
{}
~LinkedList() {}
void createList(LinkedList& list);
void insertHead(LinkedList& list, Node* temp);
void appenTail(LinkedList& list, Node* temp);
void readLine(ifstream& file, Item& item);
void readAllFile(ifstream& file, LinkedList& list);
void printOneLine(Item item);
void printAll(LinkedList list);
//void writeToFile(LinkedList& list);
void addItem(LinkedList& list);
void deleteItem(LinkedList list);
void updateItem(LinkedList& list);
void searchById(LinkedList list);
void searchByTitle(LinkedList list);
};
Finally, this is my item.cpp file:
void LinkedList::updateItem(LinkedList& list)
{
string updateId, updateTitle, updateType, updateLoan, updateNumCopy, updateFee, updateGenre;
Node node;
Node* temp = list.head;
bool found = false;
if (temp == nullptr)
{
cerr << "There are no items." << endl;
exit(EXIT_FAILURE);
}
cout << "Enter the item's id and other info you want to update below:" << endl;
cout << "ID: ";
cin.ignore();
getline(cin, updateId);
cout << "Title: ";
cin.ignore();
getline(cin, updateTitle);
cout << "Type: ";
cin.ignore();
getline(cin, updateType);
cout << "Loan type: ";
cin.ignore();
getline(cin, updateLoan);
cout << "Copy(s): ";
cin.ignore();
getline(cin, updateNumCopy);
cout << "Rental fee: ";
cin.ignore();
getline(cin, updateFee);
cout << "Rental genre: ";
cin.ignore();
getline(cin, updateGenre);
while (temp != nullptr)
{
Item item = temp->getData();
if ((_stricmp(item.getItemId().c_str(), updateId.c_str()) == 0) || (_stricmp(item.getTitle().c_str(), updateTitle.c_str()) == 0))
{
item.getItemId() = updateId;
item.getTitle() = updateTitle;
item.getType() = updateType;
item.getLoan() = updateLoan;
item.getFee() = updateFee;
item.getGenre() = updateGenre;
found = true;
}
temp = temp->getNext();
}
if (!found)
{
cerr << "Item not found." << endl;
exit(EXIT_FAILURE);
}
}
So the main problem is that inside the updateItem() function, we do not know how to make the function to update a specific variables of the object. I have tried the above updateItem function and the final result is that none of the item's information is changed.
Thank you.

Answer 1

Item item = temp->getData();
getData returns a copy and it is stored inside a new variable. You are making changes but it is not in the right variable. One solution would be to store and return a reference:
// return a reference
Item & getData() { return data; }
// store a reference
Item & item = temp->getData();