I'd like to know is it possible that two classes has attributes and can use methods of each other. For example, there're a class STUDENT and a class COURSE, a STUDENT have a list of joined courses and a COURSE have list of participants(students). I tried this:
in STUDENT.h
#include <iostream>
#include <vector>
// #include "COURSE.h"
class COURSE;
class STUDENT {
string name;
std::vector<COURSE*> listCourses;
public:
STUDENT(){};
addCourse(COURSE* &course){
listCourses.push_back(course);
course.addStudent(this);
}
string getName(){
return this->name;
}
void showCourses(){
for(COURSE* course : listCourses)
std::cout << course->getName() << std::endl;
}
};
in COURSE.h
#include <iostream>
#include <vector>
// #include "STUDENT.h"
class STUDENT;
class COURSE {
string name;
std::vector<STUDENT*> listStudents;
public:
COURSE(){}
addStudent(STUDENT* &student){
listStudents.push_back(student);
student.addCourse(this);
}
string getName(){
return this->name;
}
void showStudent(){
for(STUDENT* student : listCourses)
std::cout << student->getName() << std::endl;
}
};
If I include two classes each other, it said errors. If I just include one, just one class worked, other class has problem.
Can anyone help me to fix it and I wonder that is it necessary to use some design patterns or data structures to solve this. Thank you
CodePudding user response:
Yes, what you are attempting is possible, but not in the way you are attempting it. You need to separate your method declarations and definitions.
Also, you have a flaw in your add...
methods that will lead to endless recursion as soon as a Student
is added to a Course
or vice versa. You need to detect when the two are already linked together so that you can avoid the loop.
Try something more like this:
Student.h
#ifndef StudentH
#define StudentH
#include <vector>
#include <string>
class Course;
class Student {
std::string name;
std::vector<Course*> listCourses;
public:
Student() = default;
~Student();
std::string getName() const;
void addCourse(Course* course);
void removeCourse(Course* course);
void showCourses() const;
};
#endif
Student.cpp
#include "Student.h"
#include "Course.h"
#include <iostream>
#include <algorithm>
Student::~Student() {
for(Course* course : listCourses) {
course->removeStudent(this);
}
}
std::string Student::getName() const {
return name;
}
void Student::addCourse(Course* course) {
if (std::find(listCourses.begin(), listCourses.end(), course) == listCourses.end()) {
listCourses.push_back(course);
course->addStudent(this);
}
}
void Student::removeCourse(Course* course) {
auto iter = std::find(listCourses.begin(), listCourses.end(), course);
if (iter != listCourses.end()) {
listCourses.erase(iter);
course->removeStudent(this);
}
}
void Student::showCourses() const {
for(Course* course : listCourses) {
std::cout << course->getName() << std::endl;
}
}
Course.h
#ifndef CourseH
#define CourseH
#include <vector>
#include <string>
class Student;
class Course {
std::string name;
std::vector<Student*> listStudents;
public:
Course() = default;
~Course();
std::string getName() const;
void addStudent(Student* student);
void removeStudent(Student* student);
void showStudents() const;
};
#endif
Course.cpp
#include "Course.h"
#include "Student.h"
#include <iostream>
#include <algorithm>
Course::~Course() {
for(Student* student : listStudents) {
student->removeCourse(this);
}
}
std::string Course::getName() const {
return name;
}
void Course::addStudent(Student* student) {
if (std::find(listStudents.begin(), listStudents.end(), student) == listStudents.end()) {
listStudents.push_back(student);
student->addCourse(this);
}
}
void Course::removeStudent(Student* student) {
auto iter = std::find(listStudents.begin(), listStudents.end(), student);
if (iter != listStudents.end()) {
listStudents.erase(iter);
student->removeCourse(this);
}
}
void Course::showStudents() const {
for(Student* student : listStudents) {
std::cout << student->getName() << std::endl;
}
}