C++ 定义和使用接口类的简单模式

川长思鸟来 2022-05-11 11:50 202阅读 0赞

以一个Person类为接口类，Student类为实现类的代码为例：1. Person.h声明了Person类，PersonCreator类，并定义了一个全局变量用来创建Student对象

#pragma once
    
    class Person
    {
    public:
        virtual ~Person() {}
    
        virtual void Eat() = 0;
        virtual void Sleep() = 0;
    };
    
    class PersonCeator
    {
    public:
        ~PersonCeator();
        Person* CreateStudent();
    };
    
    extern PersonCeator* g_creator;

2. Student.cpp声明了Student类，并实现了Student类和PersonCreator类：

#include <iostream>
    #include "Person.h"
    using namespace std;
    
    class Student : Person
    {
    public:
        Student();
        virtual ~Student();
    
        virtual void Eat();
        virtual void Sleep();
    };
    
    Student::Student()
    {
        cout << "创建Student" << endl;
    }
    
    Student::~Student()
    {
        cout << "析构Student" << endl;
    }
    
    void Student::Eat()
    {
        cout << "吃饭" << endl;
    }
    
    void Student::Sleep()
    {
        cout << "睡觉" << endl;
    }
    
    Person* PersonCeator::CreateStudent()
    {
        Student* student= new Student();
        //Student student;
        return (Person*)student;
    
    }
    PersonCeator::~PersonCeator()
    {
        cout << "析构PersonCreator" << endl;
    }
    
    PersonCeator creator;
    extern PersonCeator* g_creator = &creator;//这样创建会在main函数运行结束后自动析构
    //extern PersonCeator* g_creator= new PersonCeator();//这样创建需要手动析构

3. main.cpp使用PersonCreator创建Student对象：

#include <iostream>
    #include "Person.h"
    
    int main()
    {
        Person* Tom = g_creator->CreateStudent();
        Tom->Eat();
        Tom->Sleep();
    
        delete Tom;  //手动析构
        //delete g_creator;
    
        getchar();
        return 0;
    }

实际上PersonCreator中的create()函数的返回值是Person类的指针，这样能够彻底地隐藏Student类的存在。同时，也应该注意到，一个模块很有可能是以动态库被其他模块调用，所以当对象是在本模块new时，也应当在本模块delete。所以接口类应该提供Release()方法。修改后的代码如下：1. Person.h声明了IPerson类，IPersonCreator类，并定义了一个全局变量用来创建Student对象

#pragma once
    
    class IPerson
    {
    public:
        virtual ~IPerson() {}
    
        virtual void Release() = 0;
        virtual void Eat() = 0;
        virtual void Sleep() = 0;
    };
    
    class IPersonCreator
    {
    public:
        virtual ~IPersonCreator() {}
        virtual IPerson* CreateStudent() = 0;
    };
    
    extern IPersonCreator* g_pCreator;

2. Student.cpp声明并实现了Student类和PersonCreator类：

#include <iostream>
    #include "Person.h"
    using namespace std;
    
    //
    //
    //   声明类Student和PersonCreator
    //
    //
    class Student : public IPerson
    {
    public:
        Student();
        virtual ~Student();
    
        virtual void Release();
    
        virtual void Eat();
        virtual void Sleep();
    private:
        char* name;
    };
    
    class PersonCreator : public IPersonCreator
    {
    public:
        PersonCreator();
        virtual ~PersonCreator();
        virtual IPerson* CreateStudent();
    
        void ReleasePerson(IPerson* pPerson);
    };
    
    
    PersonCreator creator;
    IPersonCreator* g_pCreator = &creator;//这样创建会在main函数运行结束后自动析构
    //
    //
    //   实现类Student
    //
    //
    Student::Student()
    {
        name = new char[255]();
        cout << "创建Student" << endl;
    }
    
    Student::~Student()
    {
        delete[] name;
        cout << "析构Student" << endl;
    }
    
    void Student::Release()
    {
        creator.ReleasePerson(this);
    }
    
    void Student::Eat()
    {
        cout << "吃饭" << endl;
    }
    
    void Student::Sleep()
    {
        cout << "睡觉" << endl;
    }
    
    //
    //
    //   实现类PersonCreator
    //
    //
    
    PersonCreator::PersonCreator()
    {
        cout << "创建PersonCreator" << endl;
    }
    
    
    PersonCreator::~PersonCreator()
    {
        cout << "析构PersonCreator" << endl;
    }
    
    
    IPerson* PersonCreator::CreateStudent()
    {
        Student* student = new Student();
        return (IPerson*)student;
    }
    
    void PersonCreator::ReleasePerson(IPerson* pPerson)
    {
        if (pPerson)
        {
            delete pPerson;
        }
    }

3. main.cpp使用接口IPersonCreator创建Student对象，使用完之后需要析构Student对象，程序结束后会自动释放PersonCreator对象。

#include <iostream>
    #include "Person.h"
    
    int main()
    {
        IPerson* Tom = g_pCreator->CreateStudent();//使用时不需强制转换了
        Tom->Eat();
        Tom->Sleep();
    
        Tom->Release();
        Tom = nullptr;
    
        getchar();
        return 0;
    }

\---------------------   
作者：文如王勃三生慧   
来源：CSDN   
原文：https://blog.csdn.net/hf19931101/article/details/78802058   
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