c++ array syntax (function returns array)

Question

Why does this code require the '&' in array syntax?

int (&returnArray(int (&arr)[42]))[42]
{
  return arr;
}

When i declare it like this

int (returnArray(int arr[42]))[42]
{
  return arr;
}

i get

error C2090: function returns array

But isn't this an array it was returning in the first example? Was it some sort of a reference to array?

I know i can also pass an array to a function, where it will decay to a pointer

int returnInt(int arr[42])
{
  return arr[0];
}

or pass it by reference

int returnInt(int (&arr)[42])
{
  return arr[0];
}

But why can't i return an array the same way it can be passed?

@john I'd guess all C++ books worth their salt should mention array value semantics. — Angew is no longer proud of SO
– Angew is no longer proud of SO, Commented May 7, 2013 at 7:42
possible duplicate of Why doesn't C++ support functions returning arrays? — Tony Delroy
– Tony Delroy, Commented May 7, 2013 at 7:46
i tried to edit the question to show that it's a little bit different from that one — spiritwolfform
– spiritwolfform, Commented May 7, 2013 at 8:03

Community · Accepted Answer · 2020-06-20 09:12:55Z

6

int (&returnArray(int (&arr)[42]))[42]

The first & means this would return a reference to the array.

This is required by the standard :

8.3.5 Functions §6 -

« Functions shall not have a return type of type array or function, although they may have a return type of type pointer or reference to such things. »

edited Jun 20, 2020 at 9:12

CommunityBot

11 silver badge

answered May 7, 2013 at 7:40

zakinster

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1 Comment

v.oddou Over a year ago

does it make sense because passing arrays as parameters decays into pointer ? thus implying the original type was always "array" and not pointer and as such cannot be expected to be returnable as a pointer type ? so this reflects the weirdness into why do we have decay at all.

Community · Accepted Answer · 2017-05-23 12:14:21Z

3

The first function is not returning an array, it's returning a reference to an array. Arrays cannot be returned by value in C++.

These topics are generally well covered in good C++ books.

edited May 23, 2017 at 12:14

CommunityBot

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answered May 7, 2013 at 7:41

Angew is no longer proud of SO

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