创建一个 Library类，包含一个 Book向量和一个Patron向量。定义一个名为Transaction 的 struet，包含一个Book对象、一个Patron对象和一个本章中定义的Date对象，表示借阅记录。在 Library 类中定义一个Transaction向量。定义向图书馆添加图书、添加读者以及借出书籍的函数。当一个读者借出一本书时,保证Library对象中有此读者和这本书的记录,否则报告错误。然后检查读者是否欠费，如果欠费就报告一个错误,否则创建一个Transaction对象，将其放人Transaction向量中。定义一个返回包含所有欠费读者姓名的向量的函数。该软件是多文件程序，按文件给出代码，在主测试文件中设置菜单，由用户手动输入图书信息，用C++设计实现，重新写一份

这里是头文件 library.h：

#ifndef LIBRARY_H
#define LIBRARY_H

#include <vector>
#include <string>
#include "book.h"
#include "patron.h"
#include "date.h"

class Library {
public:
    struct Transaction {
        Book book;
        Patron patron;
        Date date;
    };
    Library();
    void add_book(Book book);
    void add_patron(Patron patron);
    void check_out_book(Book book, Patron patron, Date date);
    std::vector<std::string> get_debtors() const;
private:
    std::vector<Book> books;
    std::vector<Patron> patrons;
    std::vector<Transaction> transactions;
};

#endif

这里是实现文件 library.cpp：

#include "library.h"

Library::Library() {}

void Library::add_book(Book book) {
    books.push_back(book);
}

void Library::add_patron(Patron patron) {
    patrons.push_back(patron);
}

void Library::check_out_book(Book book, Patron patron, Date date) {
    bool book_found = false;
    bool patron_found = false;
    for (int i = 0; i < books.size(); i++) {
        if (books[i].get_isbn() == book.get_isbn()) {
            book_found = true;
            break;
        }
    }
    for (int i = 0; i < patrons.size(); i++) {
        if (patrons[i].get_card_number() == patron.get_card_number()) {
            patron_found = true;
            if (patrons[i].get_fees_owed() > 0) {
                throw std::runtime_error("Patron owes fees");
            }
            break;
        }
    }
    if (!book_found || !patron_found) {
        throw std::runtime_error("Book or patron not found");
    }
    transactions.push_back(Transaction{book, patron, date});
}

std::vector<std::string> Library::get_debtors() const {
    std::vector<std::string> debtors;
    for (int i = 0; i < patrons.size(); i++) {
        if (patrons[i].get_fees_owed() > 0) {
            debtors.push_back(patrons[i].get_name());
        }
    }
    return debtors;
}

这里是头文件 book.h：

#ifndef BOOK_H
#define BOOK_H

#include <string>

class Book {
public:
    Book(std::string isbn, std::string title, std::string author);
    std::string get_isbn() const;
    std::string get_title() const;
    std::string get_author() const;
private:
    std::string isbn;
    std::string title;
    std::string author;
};

#endif

这里是实现文件 book.cpp：

#include "book.h"

Book::Book(std::string isbn, std::string title, std::string author) : isbn(isbn), title(title), author(author) {}

std::string Book::get_isbn() const {
    return isbn;
}

std::string Book::get_title() const {
    return title;
}

std::string Book::get_author() const {
    return author;
}

这里是头文件 patron.h：

#ifndef PATRON_H
#define PATRON_H

#include <string>

class Patron {
public:
    Patron(std::string name, std::string card_number);
    std::string get_name() const;
    std::string get_card_number() const;
    double get_fees_owed() const;
    void set_fees_owed(double fees);
private:
    std::string name;
    std::string card_number;
    double fees_owed;
};

#endif

这里是实现文件 patron.cpp：

#include "patron.h"

Patron::Patron(std::string name, std::string card_number) : name(name), card_number(card_number), fees_owed(0) {}

std::string Patron::get_name() const {
    return name;
}

std::string Patron::get_card_number() const {
    return card_number;
}

double Patron::get_fees_owed() const {
    return fees_owed;
}

void Patron::set_fees_owed(double fees) {
    fees_owed = fees;
}

这里是头文件 date.h：

#ifndef DATE_H
#define DATE_H

#include <string>

class Date {
public:
    Date(int year, int month, int day);
    std::string to_string() const;
private:
    int year;
    int month;
    int day;
};

#endif

这里是实现文件 date.cpp：

#include "date.h"

Date::Date(int year, int month, int day) : year(year), month(month), day(day) {}

std::string Date::to_string() const {
    return std::to_string(year) + "-" + std::to_string(month) + "-" + std::to_string(day);
}

这里是主测试文件 main.cpp：

#include <iostream>
#include "library.h"

int main() {
    Library library;
    std::string input;
    std::cout << "Enter book information (ISBN title author): ";
    std::getline(std::cin, input);
    std::string isbn = input.substr(0, input.find(" "));
    input.erase(0, input.find(" ") + 1);
    std::string title = input.substr(0, input.find(" "));
    input.erase(0, input.find(" ") + 1);
    std::string author = input;
    Book book(isbn, title, author);
    library.add_book(book);
    std::cout << "Enter patron information (name card number): ";
    std::getline(std::cin, input);
    std::string name = input.substr(0, input.find(" "));
    input.erase(0, input.find(" ") + 1);
    std::string card_number = input;
    Patron patron(name, card_number);
    library.add_patron(patron);
    std::cout << "Enter checkout information (ISBN card number year month day): ";
    std::getline(std::cin, input);
    isbn = input.substr(0, input.find(" "));
    input.erase(0, input.find(" ") + 1);
    card_number = input.substr(0, input.find(" "));
    input.erase(0, input.find(" ") + 1);
    int year = std::stoi(input.substr(0, input.find(" ")));
    input.erase(0, input.find(" ") + 1);
    int month = std::stoi(input.substr(0, input.find(" ")));
    input.erase(0, input.find(" ") + 1);
    int day = std::stoi(input);
    Book checkout_book("", "", "");
    Patron checkout_patron("", "");
    for (int i = 0; i < library.get_books().size(); i++) {
        if (library.get_books()[i].get_isbn() == isbn) {
            checkout_book = library.get_books()[i];
            break;
        }
    }
    for (int i = 0; i < library.get_patrons().size(); i++) {
        if (library.get_patrons()[i].get_card_number() == card_number) {
            checkout_patron = library.get_patrons()[i];
            break;
        }
    }
    try {
        library.check_out_book(checkout_book, checkout_patron, Date(year, month, day));
        std::cout << "Checkout successful" << std::endl;
    } catch (std::runtime_error& e) {
        std::cout << "Error: " << e.what() << std::endl;
    }
    std::vector<std::string> debtors = library.get_debtors();
    if (debtors.size() > 0) {
        std::cout << "The following patrons owe fees:" << std::endl;
        for (int i = 0; i < debtors.size(); i++) {
            std::cout << debtors[i] << std::endl;
        }
    }
    return 0;
}