class Book { string isbn,name,author,press; double price; public: friend ostream &operator<<(ostream &out, Book &b); friend istream &operator>>(istream &in, Book &b); }; 实现其中运算符<<、>>重载函数的定义，使其能够输入输出一个书类对象的信息。

请看下面的代码实现：

#include <iostream>
#include <string>
using namespace std;

class Book {
  string isbn, name, author, press;
  double price;

public:
  friend ostream &operator<<(ostream &out, Book &b);
  friend istream &operator>>(istream &in, Book &b);
};

ostream &operator<<(ostream &out, Book &b) {
  out << "ISBN: " << b.isbn << endl;
  out << "Name: " << b.name << endl;
  out << "Author: " << b.author << endl;
  out << "Press: " << b.press << endl;
  out << "Price: " << b.price << endl;

  return out;
}

istream &operator>>(istream &in, Book &b) {
  cout << "ISBN: ";
  in >> b.isbn;
  cout << "Name: ";
  in >> b.name;
  cout << "Author: ";
  in >> b.author;
  cout << "Press: ";
  in >> b.press;
  cout << "Price: ";
  in >> b.price;

  return in;
}

int main() {
  Book book;
  cin >> book;
  cout << book;

  return 0;
}

在这个实现中，我们使用了 `friend` 关键字来让运算符函数访问 `Book` 类的私有成员。`operator<<` 函数用于输出一个 `Book` 类对象的信息，而 `operator>>` 函数用于输入一个 `Book` 类对象的信息。在 `main` 函数中，我们通过 `cin` 输入一个 `Book` 类对象的信息，然后通过 `cout` 输出这个对象的信息。