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 = ;
     virtual int GetAge() const = ;
     virtual std::string GetClassName() const = ;
 };

 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 = ;
 };

 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"), , );
     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 ;
 }

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