访问者模式

C++

#include <iostream>
#include <list>
using namespace std;class Visitor;// 组成Computer的各组件基类
class Element
{
public:Element(string strName) : m_strName(strName) {}string GetName(){return m_strName;}// 组件接受访问者访问的接口virtual void AcceptVisitor(Visitor *pVisitor) = 0;private:// 组件的标识名称string m_strName;
};// 访问者基类，针对不同组件，提供不同的访问接口
class Visitor
{
public:virtual void VisitCPU(Element *pEle) = 0;virtual void VisitGPU(Element *pEle) = 0;virtual void VisitDISK(Element *pEle) = 0;
};// Computer类，由各组件组成，访问者访问Computer时将依次访问各组件
class Computer
{
public:~Computer(){for (Element *pElement : m_listEle){delete pElement;}}void AddElement(Element *pEle){m_listEle.push_back(pEle);}void DelElement(Element *pEle){m_listEle.remove(pEle);}// 访问者访问Computer时将依次访问各组件void AcceptVisitor(Visitor *pVisitor){for (Element *pElement : m_listEle){pElement->AcceptVisitor(pVisitor);}}private:list<Element *> m_listEle;
};// 访问者实现类，实现各自的访问方法
class VisitorA : public Visitor
{
public:void VisitCPU(Element *pEle){printf("Visitor A record CPU's name:%s\n", pEle->GetName().c_str());}void VisitGPU(Element *pEle){printf("Visitor A do nothing to GPU:%s\n", pEle->GetName().c_str());}void VisitDISK(Element *pEle){printf("Visitor A change DISK:%s\n", pEle->GetName().c_str());}
};class VisitorB : public Visitor
{
public:void VisitCPU(Element *pEle){printf("Visitor B do nothing to CPU:%s\n", pEle->GetName().c_str());}void VisitGPU(Element *pEle){printf("Visitor B record GPU's name:%s\n", pEle->GetName().c_str());}void VisitDISK(Element *pEle){printf("Visitor B do nothing to DISK:%s\n", pEle->GetName().c_str());}
};// 组件的实现类，调用访问者相应的访问方法
class CPU : public Element
{
public:CPU(string strName) : Element(strName) {}void AcceptVisitor(Visitor *pVisitor){pVisitor->VisitCPU(this);}
};class GPU : public Element
{
public:GPU(string strName) : Element(strName) {}void AcceptVisitor(Visitor *pVisitor){pVisitor->VisitGPU(this);}
};class Disk : public Element
{
public:Disk(string strName) : Element(strName) {}void AcceptVisitor(Visitor *pVisitor){pVisitor->VisitDISK(this);}
};int main()
{Computer oComputer;oComputer.AddElement(new CPU("i9-10980XE"));oComputer.AddElement(new GPU("Titan RTX"));oComputer.AddElement(new Disk("HOF PRO M.2"));VisitorA oVisitorA;VisitorB oVisitorB;oComputer.AcceptVisitor(&oVisitorA);oComputer.AcceptVisitor(&oVisitorB);return 0;
}

C

#include <stdio.h>
#include <stdlib.h>
#include <string.h>typedef struct Element Element;
typedef struct Visitor Visitor;
typedef struct Computer Computer;
typedef struct CPU CPU;
typedef struct GPU GPU;
typedef struct Disk Disk;// 组件基类
struct Element
{char *m_strName;void (*accept)(struct Element *, struct Visitor *);
};// 访问者基类
struct Visitor
{void (*visitCPU)(struct Element *);void (*visitGPU)(struct Element *);void (*visitDisk)(struct Element *);
};// Computer类
struct Computer
{struct Element **m_listEle;size_t m_listSize;size_t m_listCapacity;
};// CPU类
struct CPU
{struct Element base;
};// GPU类
struct GPU
{struct Element base;
};// Disk类
struct Disk
{struct Element base;
};// 创建组件
struct Element *createElement(const char *name, void (*accept)(struct Element *, struct Visitor *))
{struct Element *element = malloc(sizeof(struct Element));element->m_strName = strdup(name);element->accept = accept;return element;
}// 创建访问者
struct Visitor *createVisitor(void (*visitCPU)(struct Element *),void (*visitGPU)(struct Element *),void (*visitDisk)(struct Element *))
{struct Visitor *visitor = malloc(sizeof(struct Visitor));visitor->visitCPU = visitCPU;visitor->visitGPU = visitGPU;visitor->visitDisk = visitDisk;return visitor;
}// 创建Computer
struct Computer *createComputer()
{struct Computer *computer = malloc(sizeof(struct Computer));computer->m_listEle = NULL;computer->m_listSize = 0;computer->m_listCapacity = 0;return computer;
}// 添加组件到Computer
void addElement(struct Computer *computer, struct Element *element)
{if (computer->m_listSize >= computer->m_listCapacity){size_t newCapacity = computer->m_listCapacity == 0 ? 1 : computer->m_listCapacity * 2;computer->m_listEle = realloc(computer->m_listEle, newCapacity * sizeof(struct Element *));computer->m_listCapacity = newCapacity;}computer->m_listEle[computer->m_listSize++] = element;
}// 删除组件
void delElement(struct Computer *computer, struct Element *element)
{size_t i;for (i = 0; i < computer->m_listSize; i++){if (computer->m_listEle[i] == element){memmove(&computer->m_listEle[i], &computer->m_listEle[i + 1], (computer->m_listSize - i - 1) * sizeof(struct Element *));computer->m_listEle[--computer->m_listSize] = NULL;break;}}
}// 访问者访问Computer
void acceptVisitor(struct Computer *computer, struct Visitor *visitor)
{size_t i;for (i = 0; i < computer->m_listSize; i++){computer->m_listEle[i]->accept(computer->m_listEle[i], visitor);}
}// 清理Computer
void clearComputer(struct Computer *computer)
{size_t i;for (i = 0; i < computer->m_listSize; i++){free(computer->m_listEle[i]->m_strName);free(computer->m_listEle[i]);}free(computer->m_listEle);free(computer);
}// 访问者A实现
void visitorAVisitCPU(struct Element *ele)
{printf("Visitor A record CPU's name:%s\n", ele->m_strName);
}
void visitorAVisitGPU(struct Element *ele)
{printf("Visitor A do nothing to GPU:%s\n", ele->m_strName);
}
void visitorAVisitDisk(struct Element *ele)
{printf("Visitor A change DISK:%s\n", ele->m_strName);
}// 访问者B实现
void visitorBVisitCPU(struct Element *ele)
{printf("Visitor B do nothing to CPU:%s\n", ele->m_strName);
}
void visitorBVisitGPU(struct Element *ele)
{printf("Visitor B record GPU's name:%s\n", ele->m_strName);
}
void visitorBVisitDisk(struct Element *ele)
{printf("Visitor B do nothing to DISK:%s\n", ele->m_strName);
}int main()
{struct Computer *oComputer = createComputer();addElement(oComputer, createElement("i9-10980XE", visitorAVisitCPU));addElement(oComputer, createElement("Titan RTX", visitorAVisitGPU));addElement(oComputer, createElement("HOF PRO M.2", visitorAVisitDisk));struct Visitor *oVisitorA = createVisitor(visitorAVisitCPU, visitorAVisitGPU, visitorAVisitDisk);struct Visitor *oVisitorB = createVisitor(visitorBVisitCPU, visitorBVisitGPU, visitorBVisitDisk);acceptVisitor(oComputer, oVisitorA);acceptVisitor(oComputer, oVisitorB);clearComputer(oComputer);free(oVisitorA);free(oVisitorB);return 0;
}