База данных книги (простая)

#include <iostream>
#include <string>
#include <fstream>
#include <regex>
#include <algorithm>
#include <map>
using namespace std;
struct Book {
    string name;
    string genre;
    unsigned rating;
    string tostr(const string& delim = " "s) {
        return name + delim + genre + delim + to_string(rating);
    }
};
class Books {
public:
    Books(const Books&) = delete;
    Books(Books&&) = delete;
    Books& operator=(const Books&) = delete;
    Books& operator=(Books&&) = delete;
    Books() : buffer_(16U), count_(0U), books_(new Book[buffer_]) {}
    ~Books() {
        read_db_.is_open() ? read_db_.close() : void();
        this->save(db_path_);
        if (books_ != nullptr) {
            delete[] books_;
            books_ = nullptr;
        }
    }
    Book operator[](int index)const { return books_[index]; }
    void add(const Book& book) {
        if (count_ == buffer_) {
            auto books = new Book[buffer_ << 1U];
            for (auto i = 0U; i < count_; ++i) books[i] = books_[i];
            delete[] books_;
            books_ = books;
        }
        books_[count_] = book;
        ++count_;
    }
    bool load(const string& db_path) {
        read_db_.open(db_path);
        const regex re{ "#" };
        string recording;
        tuple<string, string, int> tmp;
        Book book;
        if (read_db_.is_open()) {
            this->clear_();
            while (getline(read_db_, recording)) {
                regex_token_iterator iter{ recording.begin(), recording.end(), re, -1 };
                book.name = iter->str();
                book.genre = (++iter)->str();
                book.rating = stoul((++iter)->str());
                this->add(book);
            }
            read_db_.close();
            db_path_ = db_path;
            return true;
        }
        return false;
    }
    void save(const string& db_path = ""s) {
        db_path_ = db_path.empty() ? db_path_ : db_path;
        write_db_.open(db_path_);
        if (write_db_.is_open()) {
            for (auto i = 0U; i < count_; ++i) write_db_ << books_[i].tostr("#"s) << '\n';
            write_db_.close();
            puts("Данные успешно сохранены!");
        } else {
            puts("Программе не удалось сохранить данные!");
        }
    }
    void show() {
        auto id = 0U;
        for (auto i = 0U; i < count_; ++i) cout << ++id << ". " << books_[i].tostr("; "s) << '\n';
    }
    map<unsigned, string, greater<>> interest() {
        map<string, unsigned> box;
        for (auto i = 0U; i < count_; ++i) {
            auto [genre, rating] = make_pair(books_[i].genre, books_[i].rating);
            box[genre] += rating;
        }
        map<unsigned, string, greater<>> reverse;
        for (const auto& [key, value] : box) reverse[value] = key;
        return reverse;
    }
private:
    size_t buffer_;
    size_t count_;
    Book* books_;
    string db_path_;
    ifstream read_db_;
    ofstream write_db_;
    void clear_() {
        count_ = 0;
    }
};
int main() {
    system("chcp 1251 > nul");
    Books books;
    books.add({ "«Гроза», А. Н. Островского", "трагедия", 25 });
    books.add({ "«Идеалы» Ф фон Шиллер", "элегия", 11 });
    books.add({ "«Король забавляется», В. М. Гюго", "драма", 42 });
    books.add({ "«Понедельник начинается в субботу», А. и Б. Стругацкие", "комедия", 49 });
    books.add({ "«Василий Тёркин», А. Твардовский", "поэма", 65 });
    books.add({ "«Преступление и наказание», Ф. М. Достоевский", "роман", 51 });
    books.add({ "«Как важно быть серьезным», О. Уальд", "комедия", 58 });
    books.add({ "«Божественная комедия», А. Данте", "поэма", 27 });
    books.add({ "«Гамлет», У. Шекспир", "трагедия", 56 });
    books.add({ "«Юлия, или Новая Элоиза», Ж.-Ж. Руссо", "роман", 17 });
    const auto db_path = "books_db.txt"s;
    books.save(db_path);
    books.load(db_path);
    puts("\n\tБаза данных КНИГИ\n");
    books.show();
    puts("\n\tЖанровый рейтинг\n");
    auto interest = books.interest();
    for (const auto& [rating, genre] : interest) cout << genre << " = " << rating << '\n';
    system("pause > nul");
}