C++接口与实现的抽象分离

IPerson.h

#ifndef I_PERSON_H_
#define I_PERSON_H_

#include <string>
#include <ostream>

class IPerson
{
public:
    virtual std::string GetName() const = 0;
    virtual int GetAge() const = 0;
    virtual std::string GetClassName() const = 0;
};

std::ostream& operator<<(std::ostream &os, const IPerson &person);

#endif

Person.h

#ifndef PERSON_H_
#define PERSON_H_

#include "IPerson.h"

class Person : virtual public IPerson
{
public:
    Person(const std::string &name, const int age);
    virtual ~Person();
    std::string GetName() const override;
    int GetAge() const override;
    std::string GetClassName() const override;
private:
    std::string name;
    int age;
};

#endif

Person.cpp

#include "Person.h"

Person::Person(const std::string &name, const int age) :
    name(name), 
    age(age)
{
}

Person::~Person()
{
}

std::string Person::GetName() const
{
    return name;
}

int Person::GetAge() const
{
    return age;
}

std::string Person::GetClassName() const
{
    return std::string("Person");
}

std::ostream& operator<<(std::ostream &os, const IPerson &person)
{
    os << "Name: " << person.GetName() << ", "
        << "Age: " << person.GetAge() << ", ";

    return os;
}

IStudent.h

#ifndef I_STUDENT_H_
#define I_STUDENT_H_

#include "IPerson.h"


class IStudent : virtual public IPerson
{
public:
    virtual int GetGrade() const = 0;
};

std::ostream& operator<<(std::ostream &os, const IStudent &student);

#endif

Student.h

#ifndef STUDENT_H_
#define STUDENT_H_

#include "IStudent.h"
#include "Person.h"

class Student : virtual public IStudent, public Person
{
public:
    Student(const std::string &name, const int age, const int grade);
    ~Student();

    int GetGrade() const override;
    std::string GetClassName() const override;
private:
    int grade;
};

#endif

Student.cpp

#include "Student.h"

Student::Student(const std::string &name, const int age, const int grade) :
    Person(name, age),
    grade(grade)
{
}

Student::~Student()
{
}

int Student::GetGrade() const
{
    return grade;
}

std::string Student::GetClassName() const
{
    return std::string("Student");
}

std::ostream& operator<<(std::ostream &os, const IStudent &student)
{
    const IPerson &person = student;
    os << person;
    os << "Grade: " << student.GetGrade() << ", ";

    return os;
}

main.cpp

#include <iostream>
#include "Student.h"

using namespace std;

int main()
{
    Student student(string("Leon"), 14, 8);
    cout << "Student: " << student << endl;
    
    IStudent &iStudent = student;
    cout << "IStudent: " << iStudent << endl;
    cout << "ClassName: " << iStudent.GetClassName() << endl;

    IPerson &iPerson = student;
    cout << "IPerson: " << iPerson << endl;
    cout << "ClassName: " << iPerson.GetClassName() << endl;

    cout << sizeof(IPerson) << endl;
    cout << sizeof(Person) << endl;
    cout << sizeof(IStudent) << endl;
    cout << sizeof(Student) << endl;

    return 0;
}

测试结果

Student: Name: Leon, Age: 14, Grade: 8,
IStudent: Name: Leon, Age: 14, Grade: 8,
ClassName: Student
IPerson: Name: Leon, Age: 14,
ClassName: Student
4
48
12
64