1. 抽象类

1.1. 访问者

class Apple;
class Pork;
class Visitor
{
public:virtual ~Visitor() = default;virtual void visit(Apple* apple) = 0;virtual void visit(Pork* pork) = 0;
protected:Visitor() = default;
};

1.2. 元素

//Element（抽象元素）
class Element
{
public:virtual ~Element() = default;virtual void accept(Visitor* visitor) = 0;void setPrice(const double& price){m_dPrice = price;}double getPrice(){return m_dPrice;}void setNum(const int& num){m_iNum = num;}int getNum(){return m_iNum;}void setName(const std::string& name){m_sName = name;}std::string getName(){return m_sName;}protected:Element(){m_dPrice = 0.0;m_iNum = 0;}double m_dPrice;int m_iNum;std::string m_sName;
};

2. 具体类

2.1. 元素 

//ConcreteElement（具体元素）
class Apple : public Element
{
public:Apple(const std::string& name, int price){setPrice(price);setNum(0);setName(name);std::cout << "Apple 构造函数，name = " << name << std::endl;}~Apple(){std::cout << "Apple 析构函数，name = " << m_sName << std::endl;}void accept(Visitor*) override;
private:};class Pork : public Element
{
public:Pork(const std::string& name, int price){setPrice(price);setNum(0);setName(name);std::cout << "Pork 构造函数，name = " << name << std::endl;}~Pork(){std::cout << "Pork 析构函数，name = " << m_sName << std::endl;}void accept(Visitor*) override;
private:};/// 放在 Visitor 类后
void Apple::accept(Visitor* visitor) {visitor->visit(this);
}
void Pork::accept(Visitor* visitor) {visitor->visit(this);
}

2.2. 访问者

//ConcreteVisitor（具体访问者）
class Customer : public Visitor
{
public:explicit Customer(const std::string& name){m_sName = name;std::cout << "Customer 构造函数" << std::endl;}~Customer() override{std::cout << "Customer 析构函数" << std::endl;}void setNum(Apple* apple, const int& num){apple->setNum(num);}void setNum(Pork* pork, const int& num){pork->setNum(num);}void visit(Apple* apple) override {std::cout << apple->getName() << "\t 单价: " << apple->getPrice() << "元/kg" << std::endl;}void visit(Pork* pork) override {std::cout << pork->getName() << "\t 单价: " << pork->getPrice() << "元/kg" << std::endl;}
private:std::string m_sName;
};class Cashier : public Visitor
{
public:explicit Cashier(){std::cout << "Cashier 构造函数" << std::endl;}~Cashier() override{std::cout << "Cashier 析构函数" << std::endl;}void visit(Apple* apple) override{std::string name = apple->getName();double price = apple->getPrice();int num = apple->getNum();double total = price * num;std::cout << name << "\t 总价：" << total << "元" << std::endl;}void visit(Pork* pork) override{std::string name = pork->getName();double price = pork->getPrice();int num = pork->getNum();double total = price * num;std::cout << name << "\t 总价：" << total << "元" << std::endl;}private:};

3. 对象结构

//ObjectStructure（对象结构）
class ShoppingCart
{
public:ShoppingCart(){}~ShoppingCart(){}void  addElement(Element* element){std::cout << "商品：" << element->getName() << "\t 数量：" << element->getNum() << "\t 加入购物车！" << std::endl;m_ElementVector.push_back(element);}void accept(Visitor* visitor){for (auto ele : m_ElementVector){ele->accept(visitor);}}private:std::vector<Element*> m_ElementVector;
};

4. 主函数

#include <string>
#include <vector>
#include <map>
#include <iostream> 
int main()
{Apple *apple1 = new Apple("大兴西瓜", 5);Apple *apple2 = new Apple("平谷大桃", 5);Pork *pork1 = new Pork("猪肉", 24);Pork *pork2 = new Pork("五花肉", 40);auto* cashier = new Cashier();auto* customer = new Customer(std::string("张三").c_str());customer->setNum(apple1, 3);customer->setNum(apple2, 4);customer->setNum(pork1, 1);customer->setNum(pork2, 2);auto* shoppingCart = new ShoppingCart();std::cout << "===购物车添加商品===" << std::endl;shoppingCart->addElement(apple1);shoppingCart->addElement(apple2);shoppingCart->addElement(pork1);shoppingCart->addElement(pork2);std::cout << "===顾客选择的商品===" << std::endl;shoppingCart->accept(customer);std::cout << "===收银员计算的价格===" << std::endl;shoppingCart->accept(cashier);std::cout << "========" << std::endl;delete apple1; delete apple2;delete pork1; delete pork2;delete cashier; delete customer;delete shoppingCart;getchar();return 0;
}