C语言实现C++面向对象特性

Posted 2022-08-05 顾文繁

要点：在结构体当中定义派生类对象指针解决继承问题。
例如定义一个基类：

typedef struct _Person

    char* pFName;
    char* pLName;
    //interface for function
    fptrDisplayInfo Display;
    fptrWriteToFile WriteToFile;
    fptrDelete Delete;
    void* pDerivedObj;
Person;

这里的函数均为函数指针：

//declaration of pointers to functions
typedef void (*fptrDisplayInfo)(Person*);
typedef void (*fptrWriteToFile)( Person*, const char*);
typedef void (*fptrDelete)( Person *) ;

这样就能保证通过父类访问到子类的方法，从而使下多态。
在子类中定义结构：

typedef struct _Employee Employee;
typedef struct _Employee

    Person* pBaseObj;
    char* pDepartment;
    char* pCompany;
    int nSalary;
//If there is any employee specific functions; add interface here.
Employee;

相应地，在子类中定义父类的结构体指针的方式能够访问到父类的成员变量，实现继承。
通过上述的定义，能够基本实现面向对象的三大特性：封装，继承，多态。
完整代码：

typedef struct _Person Person;
//declaration of pointers to functions
typedef void (*fptrDisplayInfo)(Person*);
typedef void (*fptrWriteToFile)( Person*, const char*);
typedef void (*fptrDelete)( Person *) ;

typedef struct _Person

    char* pFName;
    char* pLName;
    //interface for function
    fptrDisplayInfo Display;
    fptrWriteToFile WriteToFile;
    fptrDelete Delete;
    void* pDerivedObj;
Person;

Person* new_Person(const char* pFirstName,
                   const char* pLastName); //constructor
void delete_Person(Person* const pPersonObj); //destructor
void Person_DisplayInfo(Person* const pPersonObj);
void Person_WriteToFile(Person* const pPersonObj, const char* pFileName);

Person* new_Person(const char* const pFirstName, const char* const pLastName)

    Person* pObj = NULL;
    //allocating memory
    pObj = (Person*)malloc(sizeof(Person));
    if (pObj == NULL)
    
        return NULL;
    
    pObj->pFName = (char*)malloc(sizeof(char)*(strlen(pFirstName)+1));
    if (pObj->pFName == NULL)
    
        return NULL;
    
    strcpy(pObj->pFName, pFirstName);
    pObj->pLName = (char*)malloc(sizeof(char)*(strlen(pLastName)+1));
    if (pObj->pLName == NULL)
    
        return NULL;
    
    strcpy(pObj->pLName, pLastName);
    //Initializing interface for access to functions
    pObj->Delete = delete_Person;
    pObj->Display = Person_DisplayInfo;
    pObj->WriteToFile = Person_WriteToFile;
    return pObj;




void delete_Person(Person* const pPersonObj)

    printf("call Person_DisplayInfo()\\n");
    free(pPersonObj);


void Person_DisplayInfo(Person* pPersonObj)

    printf("call Person_DisplayInfo()\\n");
    printf("pFirstName:%s pLastName:%s\\n",pPersonObj->pFName,pPersonObj->pLName);


void Person_WriteToFile(Person* const pPersonObj, const char* pFileName)

    printf("call Person_WriteToFile()\\n");




typedef struct _Employee Employee;

typedef struct _Employee

    Person* pBaseObj;
    char* pDepartment;
    char* pCompany;
    int nSalary;
//If there is any employee specific functions; add interface here.
Employee;

Person* new_Employee(const char* pFirstName, const char* pLastName,
                     const char* pDepartment, const char* pCompany,
                     int nSalary); //constructor

void delete_Employee(Person* pPersonObj); //destructor
void Employee_DisplayInfo(Person* pPersonObj);
void Employee_WriteToFile(Person* const pPersonObj, const char* const pFileName);

//Employee
Person* new_Employee(const char* const pFirstName, const char* const pLastName,
                     const char* const pDepartment,
                     const char* const pCompany, int nSalary)

    Employee* pEmpObj;
    //calling base class construtor
    Person* pObj = new_Person(pFirstName, pLastName);
    //allocating memory
    pEmpObj = (Employee*)malloc(sizeof(Employee));
    if (pEmpObj == NULL)
    
        pObj->Delete(pObj);
        return NULL;
    
    pEmpObj->pBaseObj = pObj;
    pObj->pDerivedObj = pEmpObj;
    pEmpObj->pDepartment = (char*)malloc(strlen(pDepartment)+1);
    if(pEmpObj->pDepartment == NULL)
    
        return NULL;
    
    strcpy(pEmpObj->pDepartment, pDepartment);
    pEmpObj->pCompany = (char*)malloc(strlen(pCompany)+1);
    if(pEmpObj->pCompany== NULL)
    
        return NULL;
    

    strcpy(pEmpObj->pCompany, pCompany);
    pEmpObj->nSalary = nSalary;
    pObj->Delete = delete_Employee;
    pObj->Display = Employee_DisplayInfo;
    pObj->WriteToFile = Employee_WriteToFile;
    return pObj;


#define FREE(memory) if((memory))free((memory));

void delete_Employee(Person* pPersonObj)

    printf("=======================delete_Employee============================\\n");
    if(!pPersonObj) return;
    Employee* employee = (Employee*)pPersonObj->pDerivedObj;
    if(employee)
    
        FREE(employee->pCompany);
        FREE(employee->pDepartment);
        FREE(employee);
    
    delete_Person(pPersonObj);
    printf("=======================delete_Employee============================\\n");

void Employee_DisplayInfo(Person* pPersonObj)

    printf("=======================Employee_DisplayInfo============================\\n");
    Employee* employee = (Employee*)pPersonObj->pDerivedObj;
    printf("first name = %s\\n", pPersonObj->pFName);
    printf("last name = %s\\n", pPersonObj->pLName);
    printf("department name = %s\\n", employee->pDepartment);
    printf("company name = %s\\n", employee->pCompany);
    printf("salary name = %d\\n", employee->nSalary);
    printf("========================Employee_DisplayInfo===========================\\n");


void Employee_WriteToFile(Person* const pPersonObj, const char* const pFileName)




int main()


    Person* PersonObj = new_Person("pengdan", "farsight");
    Person* EmployeeObj = new_Employee("kouxiaojuan", "liuyan","HR", "TCS", 40000);
    PersonObj->Display(PersonObj);
    PersonObj->WriteToFile(PersonObj,"persondata.txt");
    PersonObj->Delete(PersonObj);
    EmployeeObj->Display(EmployeeObj);
    EmployeeObj->WriteToFile(EmployeeObj, "employeedata.txt");
    EmployeeObj->Delete(EmployeeObj);

    return 0;