Return array of pointers by reference

Question

Inside one of my classes i've got a

Reservation * availability[30] = {nullptr};

(which I of course initialize later with some values).

Nevertheless, I've got a getReservations() function which is supposed to return a reference to that array of 30 elements, so that it can be used like:

getReservations()[i] ...

How should I declare that function?

Side note: I'd personally initialize the array with = {};. It looks like you think all of the elements are initialized to the nullptr you've written, but they're actually value-initialized. — Quentin
– Quentin, Commented May 7, 2017 at 20:13
@Quentin well, value-initialization and nullptr initialization do the same thing, don't they? I agree though, it's silly to treat the first element differently. — eerorika
– eerorika, Commented May 7, 2017 at 20:15
@user2079303 yes, that's my point. There's no functional difference but it is a bit misleading. — Quentin
– Quentin, Commented May 7, 2017 at 20:16
@Quentin my point is that is it really misleading when it leads to the same result with no difference? It's just silly in my opinion. — eerorika
– eerorika, Commented May 7, 2017 at 20:18

flogram_dev · Accepted Answer · 2017-08-03 15:52:00Z

5

The syntax for declaring a function that returns the array by reference is this:

Reservation * (& getReservations())[30];

Of course, as you can see, you shouldn't use this in real life. Instead do it with a type alias:

using Reservations = Reservation * [30];

Reservations & getReservations();

Or, because arrays aren't bounds-checked anyway, just return a pointer which you can then index like an array:

Reservation * getReservations();

edited Aug 3, 2017 at 15:52

answered May 7, 2017 at 20:13

flogram_dev

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Flexo - Save the data dump · Accepted Answer · 2017-05-09 08:21:29Z

4

Reservation *(&getReservations())[30];

should do it for you.

Please remember of dangling references and pointer management.

edited May 9, 2017 at 8:21

Flexo - Save the data dump♦

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answered May 7, 2017 at 20:13

bipll

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Juan Leni · Accepted Answer · 2017-05-07 20:25:11Z

1

I would recommend you to use modern C++:

using ReservationArray = std::array<Reservation*, 30>;

ReservationArray _availability;

and to return that as:

ReservationArray& getReservations()

edited May 7, 2017 at 20:25

answered May 7, 2017 at 20:19

Juan Leni

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3 Comments

Mooing Duck Over a year ago

raw pointers are still incredibly useful in modern C++. Don't mistake "pointers" for "owning dynamic values". Those are orthogonal concepts.

Juan Leni Over a year ago

true, they are useful in some specific cases. But why would you recommend using raw pointers here?

Mooing Duck Over a year ago

You made the (unsubstantiated) assumption that these pointers own data. If they're non-owning, then unique_ptr causes double delete undefined behavior, which is very very bad. These pointers could just as likely be nullable references, in which case Reservation* is the correct thing to use.

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