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。

根据题意，以下是类Product的完整代码，包括构造函数、赋值运算符重载、大于运算符重载和流插入运算符重载：

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

class Product {
    string name;        // 产品名称
    int price;          // 产品单价
    int quantity;       // 剩余产品数量
public:
    // 构造函数
    Product(string n, int p, int q) {
        name = n;
        price = p;
        quantity = q;
    }
    
    // 赋值运算符重载
    Product operator = (const Product &p) {
        name = p.name;
        price = p.price;
        quantity = p.quantity;
        return *this;
    }
    
    // 大于运算符重载
    friend bool operator >(const Product &p1, const Product &p2) {
        return p1.price > p2.price;
    }
    
    // 流插入运算符重载
    friend ostream& operator<<(ostream &out, Product &t) {
        out << "Product Name: " << t.name << endl;
        out << "Price: " << t.price << endl;
        out << "Quantity: " << t.quantity << endl;
        return out;
    }
};

int main() {
    Product p1("Product A", 10, 20);
    Product p2("Product B", 5, 30);
    
    // 测试赋值运算符重载
    p2 = p1;
    cout << "After assign p1 to p2:\n" << p2 << endl;
    
    // 测试大于运算符重载
    if (p1 > p2) {
        cout << "p1 is more expensive than p2.\n";
    } else {
        cout << "p2 is more expensive than p1.\n";
    }
    
    // 测试流插入运算符重载
    cout << "Product Info:\n" << p1 << endl;
    
    return 0;
}

在main函数中，我们定义了两个Product对象p1和p2，并测试了赋值运算符重载、大于运算符重载和流插入运算符重载的正确性。