好，其中 date 是归还日期 格式是 年-月-日 ，给我写一个函数，即将到期的图书，还要有一个参数临期几天的。使用C语言写

以下是一个示例函数：

#include <stdio.h>
#include <time.h>

typedef struct {
    char name[50];
    char author[50];
    char publisher[50];
    char ISBN[20];
    char category[20];
    char borrower[50];
    char borrow_date[11];
    char return_date[11];
} BOOK;

int days_until_due(char *return_date, int warning_days) {
    struct tm due_time = {0};
    time_t now, due;

    sscanf(return_date, "%d-%d-%d", &due_time.tm_year, &due_time.tm_mon, &due_time.tm_mday);
    due_time.tm_year -= 1900;
    due_time.tm_mon--;

    time(&now);
    due = mktime(&due_time);

    return (int) (difftime(due, now) / (24 * 3600)) - warning_days;
}

void print_books_near_due(BOOK *books, int num_books, int warning_days) {
    int i, days_left;

    printf("The following books will be due soon:\n");
    for (i = 0; i < num_books; i++) {
        if (books[i].borrower[0] == '\0') continue;
        days_left = days_until_due(books[i].return_date, warning_days);
        if (days_left <= 0)
            printf("%s, borrowed by %s, is due today.\n", books[i].name, books[i].borrower);
        else if (days_left <= warning_days)
            printf("%s, borrowed by %s, will be due in %d day(s).\n", books[i].name, books[i].borrower, days_left);
    }
}

int main() {
    BOOK library[] = {
        {"Introduction to C Programming", "John Smith", "Publisher A", "ISBN123", "Programming", "Alice", "2022-01-01", "2022-02-01"},
        {"Learning Python", "Jane Doe", "Publisher B", "ISBN345", "Programming", "Bob", "2022-01-03", "2022-02-03"},
        {"Pride and Prejudice", "Jane Austen", "Publisher C", "ISBN678", "Fiction", "Carol", "2022-01-05", "2022-02-05"},
        {"The History of China", "David Lee", "Publisher D", "ISBN910", "History", "", "2022-01-07", "2022-02-07"}
    };
    int num_books = sizeof(library) / sizeof(BOOK);
    int warning_days = 5;

    print_books_near_due(library, num_books, warning_days);
    return 0;
}

该函数依赖于 `days_until_due` 函数，该函数接受一个日期字符串和一个警告天数，并返回收到警告时距离到期的天数。主函数中的 `print_books_near_due` 函数检查每个书籍的归还日期，并打印将到期或已到期的书籍。在此函数中，我们忽略未被借阅的书籍。