访问者模式(大话设计模式)C/C++版本

访问者模式

C++

#include 
#include 
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 
#include 
#include 

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;
}

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