Library

#include <iostream>
#include <ostream>
#include <string>
#include <utility>
#include <set>
#include <fstream>
#include <vector>
#include <sstream>

const std::string filename = "E:\\TempProject\\Database.dat";

using namespace std;

class Book {
private:
    vector<string> author_names;
    string date;
    bool is_available;
public:
    Book(string date, bool is_available);

    Book();

    vector<string> get_author_names() const;

    void add_author(const string& author_name);

    string get_date() const;

    void set_date(const string& date);

    bool get_is_available() const;

    void set_is_available(bool is_available);

    friend ostream& operator<<(ostream& stream, const Book& other);

    bool operator<(const Book& other) const;
};

Book::Book(string date, bool is_available)
    : date(std::move(date)),
    is_available(is_available) {}

Book::Book()
    : date(""),
    is_available(false) { }

vector<string> Book::get_author_names() const {
    return this->author_names;
}

void Book::add_author(const string& author_name) {
    this->author_names.push_back(author_name);
}

string Book::get_date() const {
    return this->date;
}

void Book::set_date(const string& date) {
    this->date = date;
}

bool Book::get_is_available() const {
    return this->is_available;
}

void Book::set_is_available(bool is_available) {
    this->is_available = is_available;
}

ostream& operator<<(ostream& stream, const Book& other) {

    for (const string& author : other.author_names) {
        stream << author << " ";
    }

    stream << other.date << " " << other.is_available;
    return stream;
}

bool Book::operator<(const Book& other) const {
    return this->author_names[0] < other.author_names[0];
}

class Library {
private:
    int count_books = 0;
public:
    set<Book> books;
};

int main() {
    Library library = Library();

    ifstream input(filename);

    string line;

    while (getline(input, line)) {

        istringstream reader(line);

        string str;

        std::vector<string> parsedWords;

        while (reader >> str) {
            parsedWords.push_back(str);
        }

        Book book(parsedWords[parsedWords.size() - 2], parsedWords[parsedWords.size() - 1] == "true");

        for (int i = 0; i < parsedWords.size() - 2; ++i) {
            book.add_author(parsedWords[i]);
        }

        library.books.insert(book);
    }

    std::cout << "Books by authors: " << std::endl;

    for (const auto& item : library.books) {
        cout << item << endl;
    }

    std::cout << std::endl;
    std::cout << "Enter date in following format -> dd.MM.yyyy: ";
    string date;
    cin >> date;

    std::cout << "Books taken by given date: " << std::endl;

    for (const auto& item : library.books) {
        if (item.get_date() == date) {
            cout << item << endl;
        }
    }

    ofstream out("ManyAuthorsOut.dat");

    for (const auto& item : library.books) {
        if (item.get_author_names().size() > 1) {
            out << item;
        }
    }
}