C++: set multiple variables from array

Question

I have the following program:

#include <iostream>
using namespace std;

int main()
{
    int array[] = {1, 2, 3};
    int a = array[0],
        b = array[1],
        c = array[2];

    cout << c << endl;
}

This prints 3, so far so good. But I wonder if there is a more elegant syntax for declaring multiple variables from an array at once. For example (just an idea, does not compile):

int [a, b, c] = array;

Is there any feature like this in C++ or one of the new standards? I can't be the only one looking it.

Alternatively: what is your most elegant way to set multiple variables from an array at once?

I think it would be nice to tell us more what you want to do with those variables or what do you to do after that — Ja_cpp
– Ja_cpp, Commented Jul 6, 2017 at 19:47
Is there a reason you cannot use the array directly? Is an array really the most appropriate structure for your actual problem? Arrays are intended for a list of items. If the data is instead a collection of related data, a class or struct is more appropriate. — Code-Apprentice
– Code-Apprentice, Commented Jul 6, 2017 at 19:50
Depends: In my project I have a data array to begin with (different author). But in general I agree, a struct would have been the better choice obviously. — mreichelt
– mreichelt, Commented Jul 6, 2017 at 20:01

Vittorio Romeo · Accepted Answer · 2017-07-06 19:50:26Z

7

In C++17 you can use structured bindings - their syntax is very similar to what you have posted:

auto [a, b, c] = array;

live example on wandbox

The closest thing to that in C++11/14 is std::tie, but it unfortunately doesn't work with arrays: it only supports std::tuple. You could however use metaprogramming to create an utility that creates a tuple from an array, and then use tie on it. There's a possible implementation in this answer by W.F..

edited Jul 6, 2017 at 19:50

answered Jul 6, 2017 at 19:47

Vittorio Romeo

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1 Comment

mreichelt Over a year ago

Wow, that was fast! Good to see this is actually coming. Now let's hope the C++17 standard is finalized fast. :)

NathanOliver · Accepted Answer · 2017-07-06 19:57:01Z

3

What you are looking for is called structured bindings and it will be available in C++17. They will allow you to create references to the elements of arrays, certain classes/structs and tuple like objects.

Since your looking for a pre C++17 solution really the best you can do is use std::tie to construct tuples that refer to what you want to assign like

int array[] = {1, 2, 3};
int a, b, c;
std::tie(a, b, c) = std::tie(array[0], array[1], array[2])

But that really doesn't save you much.

edited Jul 6, 2017 at 19:57

answered Jul 6, 2017 at 19:50

NathanOliver

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