C++ Cohesion with class Date - c++

Question

I'm preparing for an exam of c++. In the last test I failed the cohesion between a class that had the Date date_event as a variable.
How to create different constructors of class P if the class P need an object Data to create an object of the class( the one with no parameters, the one with all the parameters and the copy constructor)?
Also i didn't write this Date actual class. Is it correct to write constructors like that ?
How should giorno(0) , month(0) etc work properly ?
(giorno=day, mese=month, anno= year)
#ifndef DATA_H
#define DATA_H
#include <iostream>
#include <cstring>
using namespace std;
class Data{
friend ostream& operator<<(ostream&, const Data&);
friend istream& operator>>(istream&, Data&);
protected:
int giorno;
int mese;
int anno;
public:
Data(): giorno(0), mese(0), anno(0){}
Data(const int& g, const int& m, const int& a): giorno(g), mese(m), anno(a){}
Data(const Data& D) : giorno(D.giorno), mese(D.mese), anno(D.anno){}
//...
};
#include "Data.h"
class P{
protected:
Data birthday;
public:
P();
P(const int, const int, const int); //i should pass day, month, year right?
P(const P&);
}

Answer 1

Well the question is not clear, but several things can be said.
General
Avoid using namespace std; and use the namespace directly. E.g. friend std::ostream& operator<<(std::ostream&, const Data&);
I suppose this is not the original code, but just in case : don't forget your header guards #ifndef CLASSNAME_H, #define CLASSNAME_H & #endif /* CLASSNAME_H */
Date class
You can implement the constructor that way, but prefer implementing them in the .cpp file.
It is unnecessary to pass the integer parameters as references. Use this for big parameters, from strings to whole objects.
Prefer English for code, even if your colleagues/reviewers/professors are not English. It is always preferred in computer science. This is valid for variable/function names, but also for comments.
P(erson) class
Give your parameters names. Often people that will use your code will only read the headers, so the headers must be as self-explanatory as possible.
For the P contractor, try this :
class Date {
public:
Date(const int pDay, const int pMonth, const int pYear);
Date(const Date &pDate);
/* Getters */
int day(void) const;
int month(void) const;
int year(void) const;
/* Setters */
void setDay(const int pDay);
void setMonth(const int pMonth);
void setYear(const int pYear);
protected:
int mDay;
int mMonth;
int mYear;
};
class Person {
public:
Person(const int pDay, const int pMonth, const int pYear);
Person(const Person &pPerson);
/* Getters */
Date birthday(void) const;
/* Setters */
void setBirthday(const int pDay, const int pMonth, const int pYear);
void setBirthday(const Date &pDate);
protected:
Date mBirthday;
};
Date::Date(const int pDay, const int pMonth, const int pYear):
mDay(pDay),
mMonth(pMonth),
mYear(pYear)
{
/* Empty */
}
Date::Date(const Date &pDate) :
mDay(pDate.day()),
mMonth(pDate.month()),
mYear(pDate.year())
{
/* Empty */
}
int Date::day(void) const {
return mDay;
}
int Date::month(void) const {
return mMonth;
}
int Date::year(void) const {
return mYear;
}
/* Setters */
void Date::setDay(const int pDay) {
mDay = pDay;
}
void Date::setMonth(const int pMonth) {
mMonth = pMonth;
}
void Date::setYear(const int pYear) {
mYear = pYear;
}
Person::Person(const int pDay, const int pMonth, const int pYear):
mBirthday(pDay, pMonth, pYear)
{
/* Empty */
}
Person::Person(const Person &pPerson):
mBirthday(pPerson.birthday().day(), pPerson.birthday().month(), pPerson.birthday().year())
{
/* Empty */
}
Date Person::birthday(void) const {
return mBirthday;
}
void Person::setBirthday(const int pDay, const int pMonth, const int pYear) {
mBirthday.setDay(pDay);
mBirthday.setMonth(pMonth);
mBirthday.setYear(pYear);
}
void Person::setBirthday(const Date &pDate) {
mBirthday.setDay(pDate.day());
mBirthday.setMonth(pDate.month());
mBirthday.setYear(pDate.year());
}
Please note that there are lots of ways to do this in a prettier fashion, and with less data copies.