c++ - set object to array of pointers to the class of the object

Question

I have a class name MyDate with the following members and methods:

class MyDate
{
    public:
        MyDate();
        void setDay(int d);
        void setMonth(int m);
        void setYear(int y);
        void set(int day_, int month_, int year_);
        void print ();

    private:
    int day;
    int month;
    int year;

};

I have another class names Calendar which has an array of pointers to MyDate.

class Calendar 
{
    public:
        Calendar() ;
        void setDate (int num);
        bool isFree(int num_);
        int firstFree();
        void insertDate(MyDate my_date_);

        void print ();

    private:
        std::array<MyDate*, 30> m_dates;

};

I implement the insert function in the following way:

void Calendar :: insertDate(MyDate my_date)
{
int f = firstFree()-1 ;//the first free index in the array
*m_dates[f]=my_date; //is there a way to implement it without getters from //MyDate class??
}

I know that I can't do *m_dates[f]=my_date;--->just to explain what I have to implement. is there a way to implement it without getters from MyDate class??

If I understand well, you have to provide an overload of `operator=` and a copy constructor (rule of 5 says you have to implement also destructor, moving assignment and moving constructor). Also, with C++11 I encourage you to use `std::shared_ptr` for this — Garf365, Mar 08 '16 at 10:50
Why do you need an array of pointers? Why can't the array just be `MyDate`s? — Simple, Mar 08 '16 at 10:53
@Garf365- where I have to provide it. In the MyDate class? And what do you mean by copy constructor? — sarit rotshild, Mar 08 '16 at 10:53
@saritrotshild Why does `Calendar` inherit from `MyDate`? That doesn't make sense. — πάντα ῥεῖ, Mar 08 '16 at 10:56
@ πάντα ῥεῖ- may be it shouldn't...I am new to cpp. What would you suggest? — sarit rotshild, Mar 08 '16 at 10:58
@saritrotshild I'd recommend you think again: _Is a calendar a date?_ — πάντα ῥεῖ, Mar 08 '16 at 11:02
@πάνταῥεῖ Private inheritance: does it model "is-a", or "has-a"? — juanchopanza, Mar 08 '16 at 11:02
@saritrotshild I would suggest no inheritance at all, and a calendar that contains `MyDate`, not `MyDate*`. — molbdnilo, Mar 08 '16 at 11:03
@saritrotshild I believe the good man suggested is that a Calendar is a composition of dates, not a specialization of a date :) (composition = it has an array of dates , specialization - is a kind of a date). — MichaelCMS, Mar 08 '16 at 11:03
@juanchopanza It's a good rule of thumb. Even the private inheritance still makes no sense. — πάντα ῥεῖ, Mar 08 '16 at 11:04
If you're not familiar with terms like "copy constructor", you should look [here](http://stackoverflow.com/questions/388242/the-definitive-c-book-guide-and-list). — molbdnilo, Mar 08 '16 at 11:04
@saritrotshild well then have an array , just don't extend MyDate :). — MichaelCMS, Mar 08 '16 at 11:06
Is this some kind of home work question? If that is the case, what is the full question? And what is the purpose that this Calendar has to solve? — Senthil Babu, Mar 08 '16 at 11:32
@Senthil Babu- it's part of an exercise. It's 2 pages exercise...the purpose of the calender is to have an array of pointers to MyDate so the user can insert to it MyDate object and manpulate the array (inser, delete, print) — sarit rotshild, Mar 08 '16 at 11:50

score 1 · Answer 1 · answered Mar 08 '16 at 11:04

1

You can't use *m_dates[f]=my_date; because the array only has pointers, so you still need to provide storage space for the actual objects. If you can and want to use smart an array of smart pointers (std::array<std::shared_ptr<MyDate>, 30> m_dates;) , you can use m_dates[f].reset(new MyDate(my_date));, otherwise you have to take care of memory management.

answered Mar 08 '16 at 11:04

stefaanv

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@stefaanv- but the question is how should I implement the assignment without getters? – sarit rotshild Mar 08 '16 at 11:10
@saritrotshild: there are no getters in my answer. You can do `MyDate date = oldDate;`, but when using pointers, you have to provide storage space. – stefaanv Mar 08 '16 at 11:13
@ stefaanv- what to you mean by provide storage spaces? please demonstrate. – sarit rotshild Mar 08 '16 at 11:15
A pointer can either point to some existing objects on which the pointer normally has no ownership, or the pointer points to an object that is new-ed as in m answer, where storage space is allocated and the values of my_data are copied to. – stefaanv Mar 08 '16 at 12:14
@saritrotshild: smart pointers: `m_dates[f].reset(new MyDate(my_date));`, ordinary pointers: `m_dates[f] = new MyDate(my_date);` with extra code to make sure you don't leak memory if m_data[f] already points to a new-ed object. The smart pointer case was already in my answer. – stefaanv Mar 08 '16 at 13:28

score 0 · Answer 2 · answered Mar 08 '16 at 11:17

First of all your array is keeping the pointers to the mydate objects and you have to properly manage the data. If I look at the interface that you use to insertDate, insertDate(myDate *my_date) would have been clear and you can use simply m_dates[f]=my_date to set the values to the array. You might have to make sure the pointers which are set valid during the program and myData objects are properly managed if your intention is to keep pointers. As mentioned in one comment in C++11 you can take the advantage of shared_pointers so you do not have to manage memory explicitly.

c++ - set object to array of pointers to the class of the object

2 Answers2