C++ Update Object attributes using set function

Question

I'm writing a bookshop program. The program stores a number of books with their associated values (title, price, isbn, author) in a vector. One of the functions I'm trying to write is to search the vector by isbn and update the values of whichever book matches. Here is my code

void UpdateOnIsbn(vector <CBooks> booklist)
{
    string searchisbn;
    char response;
    string booktitle;
    string author;
    double price;
    string ISBN;

    cout << "Please enter an ISBN to be searched: ";
    cin >> searchisbn;

    for (int i = 0; i < booklist.size(); i++)
    {
        if (booklist[i].HasISBN(searchisbn))
        {
            booklist[i].Display();

            cout << "Would you like to update the details of this book? (Y/N): ";
            cin >> response;

            if (response != 'n' && response != 'N')
            {


                    cout << endl << "Please Enter New Title for book: ";
                    cin >> booktitle;
                    booklist[i].SetTitle(booktitle);

                    cout << endl << "Please Enter New Author ";
                    cin >> author;
                    booklist[i].SetAuthor(author);

                    cout << endl << "Please Enter New Price ";
                    cin >> price;
                    booklist[i].SetPrice(price);

                    cout << endl << "Please Enter New ISBN ";
                    cin >> ISBN;
                    booklist[i].SetISBN(ISBN);





            } 

        }
    }
}

The function seems to work as it looks for new values to be entered but after it runs the old values are not replaced when I display the books again. Please help

Here is an example of one of the set functions:

void CBooks::SetPrice(double NewPrice)
{
    m_Price = NewPrice;
}

What did you observe when stepping through your code with the debugger? — πάντα ῥεῖ, Oct 02 '15 at 14:47

score 1 · Answer 1 · answered Oct 02 '15 at 14:47

1

You are passing a copy of booklist so you are modifying the copy not the original object.

Try passing a reference to the function void UpdateOnIsbn(vector <CBooks>& booklist)

answered Oct 02 '15 at 14:47

Lucacox

195
1
9

score 0 · Accepted Answer · answered Oct 02 '15 at 14:47

0

You need to pass booklist by reference:

void UpdateOnIsbn(vector <CBooks>& booklist)

Otherwise the vector is copied and only this copy is modified.

answered Oct 02 '15 at 14:47

m.s.

16,063
7
53
88

Thanks this worked, pass by reference is an area I've been finding confusing – user3429270 Oct 02 '15 at 14:57

C++ Update Object attributes using set function

2 Answers2