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。多文件程序，按文件给出代码，测试文件用户手动录入信息的操作，用户可以手动添加信息

这是一个多文件程序，需要分别创建 Library.h，Library.cpp，Transaction.h，Transaction.cpp，Book.h，Book.cpp，Patron.h 和 Patron.cpp 这些文件。

首先是 Book.h 文件：

#pragma once
#include <string>

class Book {
private:
    std::string title;
    std::string author;
    std::string isbn;
    bool checkedOut;

public:
    Book(std::string title, std::string author, std::string isbn);
    std::string getTitle();
    std::string getAuthor();
    std::string getISBN();
    bool isCheckedOut();
    void checkOut();
    void checkIn();
};

然后是 Book.cpp 文件：

#include "Book.h"

Book::Book(std::string title, std::string author, std::string isbn) {
    this->title = title;
    this->author = author;
    this->isbn = isbn;
    checkedOut = false;
}

std::string Book::getTitle() {
    return title;
}

std::string Book::getAuthor() {
    return author;
}

std::string Book::getISBN() {
    return isbn;
}

bool Book::isCheckedOut() {
    return checkedOut;
}

void Book::checkOut() {
    checkedOut = true;
}

void Book::checkIn() {
    checkedOut = false;
}

接下来是 Patron.h 文件：

#pragma once
#include <string>

class Patron {
private:
    std::string name;
    double fees;

public:
    Patron(std::string name);
    std::string getName();
    double getFees();
    void addFee(double fee);
    void payFees(double payment);
};

然后是 Patron.cpp 文件：

#include "Patron.h"

Patron::Patron(std::string name) {
    this->name = name;
    fees = 0.0;
}

std::string Patron::getName() {
    return name;
}

double Patron::getFees() {
    return fees;
}

void Patron::addFee(double fee) {
    fees += fee;
}

void Patron::payFees(double payment) {
    fees -= payment;
}

接下来是 Transaction.h 文件：

#pragma once
#include "Book.h"
#include "Patron.h"
#include "Date.h"

struct Transaction {
    Book book;
    Patron patron;
    Date date;
};

然后是 Transaction.cpp 文件：

#include "Transaction.h"

// 空文件，不需要实现

接下来是 Library.h 文件：

#pragma once
#include <vector>
#include "Book.h"
#include "Patron.h"
#include "Transaction.h"

class Library {
private:
    std::vector<Book> books;
    std::vector<Patron> patrons;
    std::vector<Transaction> transactions;

public:
    void addBook(Book book);
    void addPatron(Patron patron);
    void checkOutBook(Book book, Patron patron, Date date);
    std::vector<std::string> getOutstandingFees();
};

然后是 Library.cpp 文件：

#include "Library.h"
#include <algorithm>

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

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

void Library::checkOutBook(Book book, Patron patron, Date date) {
    auto bookIter = std::find(books.begin(), books.end(), book);
    auto patronIter = std::find(patrons.begin(), patrons.end(), patron);

    if (bookIter == books.end() || patronIter == patrons.end()) {
        throw std::runtime_error("Book or patron not found in library");
    }

    if (patron.getFees() > 0.0) {
        throw std::runtime_error("Patron has outstanding fees");
    }

    book.checkOut();
    transactions.push_back({book, patron, date});
}

std::vector<std::string> Library::getOutstandingFees() {
    std::vector<std::string> names;

    for (auto patron : patrons) {
        if (patron.getFees() > 0.0) {
            names.push_back(patron.getName());
        }
    }

    return names;
}

最后是 Date.h 文件：

#pragma once

class Date {
private:
    int day;
    int month;
    int year;

public:
    Date(int day, int month, int year);
};

然后是 Date.cpp 文件：

#include "Date.h"

Date::Date(int day, int month, int year) {
    this->day = day;
    this->month = month;
    this->year = year;
}

这些文件都是需要编译的，然后在测试文件中包含 Library.h，Date.h，Book.h 和 Patron.h 即可使用 Library 类。

下面是一个示例的测试文件：

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

int main() {
    Library library;

    Book book1("The Great Gatsby", "F. Scott Fitzgerald", "978-3-16-148410-0");
    Book book2("To Kill a Mockingbird", "Harper Lee", "978-3-16-148410-1");
    Book book3("1984", "George Orwell", "978-3-16-148410-2");

    Patron patron1("John Smith");
    Patron patron2("Jane Doe");

    library.addBook(book1);
    library.addBook(book2);
    library.addBook(book3);

    library.addPatron(patron1);
    library.addPatron(patron2);

    try {
        library.checkOutBook(book1, patron1, Date(1, 1, 2022));
        std::cout << "Book checked out successfully" << std::endl;
    } catch (std::runtime_error& e) {
        std::cout << e.what() << std::endl;
    }

    try {
        library.checkOutBook(book3, patron2, Date(1, 1, 2022));
        std::cout << "Book checked out successfully" << std::endl;
    } catch (std::runtime_error& e) {
        std::cout << e.what() << std::endl;
    }

    try {
        library.checkOutBook(book2, patron1, Date(1, 1, 2022));
        std::cout << "Book checked out successfully" << std::endl;
    } catch (std::runtime_error& e) {
        std::cout << e.what() << std::endl;
    }

    std::vector<std::string> fees = library.getOutstandingFees();

    if (fees.size() == 0) {
        std::cout << "No outstanding fees" << std::endl;
    } else {
        std::cout << "Outstanding fees:" << std::endl;

        for (auto name : fees) {
            std::cout << "- " << name << std::endl;
        }
    }

    return 0;
}

这个测试文件会将三本书和两个读者添加到图书馆中，然后尝试借阅这些书。如果读者有未支付的费用，就无法借阅书籍。最后输出所有有未支付费用的读者的姓名。