writing file in header c++

Question

I have 3 files, book.h, book.cpp, bookdriver.cpp. I want to know if the ISBNs in a list are found in the array using binary search.

book.h:

using namespace std;
ofstream fout("output2.txt");
class Book
{
    string author;          // A string for the name of the author
    string title;           //A string for the book title
    int ISBN;               //A long integer for the ISBN

    public:
        Book();                         //A default constructor
        void print();
        int getISBN() const;            //A const function GetISBN that returns the integer containing the ISBN.
        int binary_search(Book, int, int, int);
};

book.cpp- also includes print function which uses fout

#include "book.h"
   //iterative binary search function, returns location of ISBN in array if present
int Book::binary_search(Book arr[], int x, int n, int ISBN)
{
    while (n >= x)
    {
        int midpt = x + (n - x) / 2;
        //if ISBN is in midpoint
        if (arr[midpt].getISBN() == ISBN)
        {
            return midpt;
        }
        //if ISBN is greater than midpoint, ignore left side of array
        if (arr[midpt].getISBN() < ISBN)
        {
            x = midpt + 1;
        }
        //if ISBN is smaller, ignore right side of array
        else
        {
            n = midpt - 1;
        }
    }

    //if ISBN not present
    return -1;
}

bookdriver.cpp

#include "book.h"

const int num = 10; //number of book objects the array should hold *can be changed*
int main()
{
    Book book_array[num] = {};  //array can hold num book objects

    for (int c = 0; c < num; c++)
    {
        book_array[c] = Book();
        book_array[c].getData(data);        //reading book information
    }

    //read file
    ifstream fin("bookISBN.txt");
    int find_ISBN;

    while (fin >> find_ISBN)
    {
        bool match = false;
        int count = 0;
        int result = binary_search(book_array[10], 0, num - 1, find_ISBN); //error here


        if (result == -1)   //if ISBN not found
        {
            fout << "Sorry, the ISBN " << find_ISBN << " is not found." << endl;
        }
        else
        {
            fout << "The ISBN " << find_ISBN << " is found in the system!" << endl;
        }
        count++;

    }
    return 0;
}

I'm using fout in both book.cpp and bookdriver.cpp so I have ofstream fout (output2.txt) in the header but I'm getting linker errors(Error LNK2005) in vs.

I think because of the one definition rule, fout is defined twice?

There are two distinct questions here. Please ask each one specifically in separate questions, with just enough context for people to understand. The first would provide details of your compiler/build system/toolchain and the specific linker error you're getting. The second would be about how to pass an array to a function in C++ (though you can definitely just google that one) — JMAA, Jul 29 '18 at 21:06
Stuff like `Book book_array[num] = {};` isn't valid C++, because [C++ doesn't have variable length arrays](https://stackoverflow.com/q/1887097/9254539). Your code only compiles because of a GCC non-standard extension. You should use an `std::vector` instead to make your code portable and avoid blowing out the stack. — eesiraed, Jul 29 '18 at 21:34

jackw11111 · Answer 1 · 2018-07-30T04:51:47.960

Here's a start:

#include <iostream>
#include <fstream>
using namespace std;

const int num = 2;

class Book
{
public:
    Book(){};
    string author;
    string title;
    int ISBN = 0;
    int data;
};

int binary_search (Book arr[num], int x, int n, int ISBN, int overflow)
{
    int mid = (x + n) / 2;

    if (x == mid || n == mid)
        overflow++;

    if (overflow > 100)
        return false;

    if (arr[mid].ISBN > ISBN)
        return binary_search(arr, x , mid, ISBN, overflow);

    else if (arr[mid].ISBN < ISBN)
        return binary_search(arr, mid, n , ISBN, overflow);

    return true;
}

int main() {

    ofstream fout("output2.txt");
    ifstream fin("bookISBN.txt");

    int find_ISBN;

    Book book1;
    book1.title = "Alice in Wonderland";
    book1.author = "C.S. Lewis";
    book1.ISBN = 1;

    Book book2;
    book2.title = "Wuthering Heights";
    book2.author = "Emily Bronte";
    book2.ISBN = 2;

    Book book3;
    book3.title = "Moby Dick";
    book3.author = "Herman Melville";
    book3.ISBN = 25;

    Book book_array[num] = {book1, book2};

    while (fin >> find_ISBN)
    {
        int result = binary_search(book_array, 0, num, find_ISBN, 0);

        if (result == false)
        {
            fout << "Sorry, the ISBN " << find_ISBN << " is not found." << endl;
        }
        else
        { 
            fout << "The ISBN " << find_ISBN << " is found in the system!" << endl;
        }
    }

    fin.close();
    fout.close();

    return 1;
}

writing file in header c++

1 Answers1