I want to keep track of the number of students in my system so, My idea was to make a static datamember in the "StudentController" class called "_numOfStudents" and increment it with the Student's constructor but it didn't work so, I moved it into the "Student" class and made that when a Student object is created the number increment by the help of the constructor. The problem is: isn't it not the Student class's business to know how many students are there thus breaking the principle of least privilege. what can I do better to keep track of the student objects' count.

    Student(string firstName, string lastName, int age,vector<float>&subjects)//Student conctructor
{
    SetFirstName(firstName);
    setLastName(lastName);
    SetAge(age);
    SetMarks(subjects);
    this->m_id  ;
    StudentController::_numberOfStudents  ;
}



    class StudentController//this is where i declared the static data member
{
private:
list<Student> _students;
public:
    static int _numberOfStudents;

    StudentController() {};
    StudentController(list<Student>& st) :_students(st) {};

        }
    }   
};

int StudentController::_numberOfStudents = 0;

CodePudding user response：

Maybe keeping track of the students shouldn't be the role of the Student class itself. Instead it should be the role of a separate Classroom object:

struct Student;
struct Classroom {
    void add(Student&) {
        m_count  ;
    }

    size_t count() const { return m_count; }
private:
    size_t m_count{0};
};

struct Student {
    Student(Classroom& classroom) {
        classroom.add(*this);
    }
};

int main()
{
    Classroom classroom;

    Student alice{classroom};
    Student bob{classroom};

    assert(classroom.count() == 2);
}

CodePudding user response：

When you try to do StudentController::_numberOfStudents ; in the constructor, the StudentController class is not yet defined, therefore the compiler doesn't know about that class and its static member.