How to return array in C++ not a pointer? [duplicate]

Question

I know how to return a pointer which points to the first element of the array, but my question is how would I return actual array, not a pointer to that array if that is even possible.

Similarly to how would I pass array to a function by reference:

void print_arr(int (&arr) [3])
{
    for(size_t i = 0; i < 3; ++i)
        std::cout << arr[i] << ' ';
}

I thought something like this:

int(&)[3] func(int (&arr) [3])
{
    // some code...
    return arr;
}

But it doesn't work. Here is the code in online compiler.

I am aware of them but I was wondering if there is a simpler solution. — Kesto2
– Kesto2, Commented Jun 11, 2023 at 16:42
You could write : auto get_array() { std::array<int,3> values{1,2,3}; return values; } Do not worry about returning what seems to be a "local" variable. C++ has something called Copy elission which means that your array will not be copied when it is returned. So it is a fast solution. And for your print function : void print(const std::array<int,3>&> values) The & means a reference (so no copy) and the const makes sure you cannot accidentally modify the content of values while printing. — Pepijn Kramer
– Pepijn Kramer, Commented Jun 11, 2023 at 16:56

CPlus · Accepted Answer · 2023-06-11 16:40:19Z

0

You cannot 'return arrays' directly in C or C++. One way you can use to get around that is declare a struct/union containing the array.

union arrayint3 {
    int i[3];
};
arrayint3 func(int(&arr)[3]) {
    arrayint3 arr = {.i = {1, 2, 3}};
    return arr;
}

You can also return an std::array. According to the linked Q&A:

Is it legal to return std::array by value, like so?
std::array<int, 3> f() {
    return std::array<int, 3> {1, 2, 3};
}

Yes it's legal.

answered Jun 11, 2023 at 16:40

CPlus

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4 Comments

Pepijn Kramer Over a year ago

I would say forget about your first solution and stick with std::array. In current C++ do NOT use unions : use std::variant. See P.4 C++ core coding guidlines

CPlus Over a year ago

@PepijnKramer Only use the first solution if pure-C compatibility is required.

Pepijn Kramer Over a year ago

I assumed this was a pure C++ question :) But yes union is one of those backward compatibility "left over" thingies.

john Over a year ago

@user16217248 What's the benefit of using a union rather than a struct?

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