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, May 07 '13 at 07:42
possible duplicate of [Why doesn't C++ support functions returning arrays?](http://stackoverflow.com/questions/5157439/why-doesnt-c-support-functions-returning-arrays) — Tony Delroy, May 07 '13 at 07:46
i tried to edit the question to show that it's a little bit different from that one — spiritwolfform, May 07 '13 at 08:03

score 6 · Accepted Answer · edited Jun 20 '20 at 09:12

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 '20 at 09:12

Community

1
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answered May 07 '13 at 07:40

zakinster

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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. – v.oddou Apr 23 '15 at 05:16

score 3 · Answer 2 · edited May 23 '17 at 12:14

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 '17 at 12:14

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answered May 07 '13 at 07:41

Angew is no longer proud of SO

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c++ array syntax (function returns array)

2 Answers2