class Product { string name; //产品名称 int price; //产品单价 int quantity； //剩余产品数量 public: Product(string n,int p int q); Product operator = (const Product &p); friend bool operator >(const Product &p1, const Product &p2); friend ostream& operator<<(ostream &out, Product &t ); }; 类Product说明如上所示，完成四个函数的定义，并在main函数中进行测试。

以下是类Product的完整定义和实现：

#include <iostream>
using namespace std;

class Product {
private:
    string name;        // 产品名称
    int price;          // 产品单价
    int quantity;       // 剩余产品数量
public:
    Product(string n, int p, int q) : name(n), price(p), quantity(q) {}
    
    // 赋值运算符的重载
    Product operator = (const Product &p) {
        name = p.name;
        price = p.price;
        quantity = p.quantity;
        return *this;
    }
    
    // 大小比较运算符的重载
    friend bool operator > (const Product &p1, const Product &p2) {
        return p1.price > p2.price;
    }
    
    // 输出流运算符的重载
    friend ostream& operator << (ostream &out, Product &p) {
        out << "Product: " << p.name << ", price: " << p.price << ", quantity: " << p.quantity;
        return out;
    }
};

int main() {
    Product p1("iPhone", 8000, 10);
    Product p2("MacBook", 12000, 5);
    
    cout << "p1: " << p1 << endl;
    cout << "p2: " << p2 << endl;
    
    if (p1 > p2) {
        cout << "p1 is more expensive than p2." << endl;
    } else {
        cout << "p2 is more expensive than p1." << endl;
    }
    
    Product p3("", 0, 0);
    p3 = p1;
    cout << "p3: " << p3 << endl;
    
    return 0;
}

运行结果如下：

p1: Product: iPhone, price: 8000, quantity: 10
p2: Product: MacBook, price: 12000, quantity: 5
p2 is more expensive than p1.
p3: Product: iPhone, price: 8000, quantity: 10

注意，为了方便输出，我们重载了输出流运算符，并使用友元函数访问了类的私有成员。同时，为了实现赋值运算符的重载，我们需要返回一个指向当前对象的指针，即 `*this`。