Initialize an array in a struct [duplicate]

Question

Is there already a way where I can initialize an array directly in a struct? Like this:

struct S { int arr[50] = {5}; }

I know this only initializes the first element of the array, but is there any way to write something similar with g++ but that can initialize all elements of the array with 5?

I've read that with gcc we can use designated intializers int arr[50] = {[0 ... 49] = 5}; but this won't be possible in C++.

It is possible by providing your own constructor. You'd need to explain why (you think) that is not good enough if you want a different answer — UnholySheep
– UnholySheep, Commented Feb 13, 2022 at 0:20
Can you please give me an example how is it possible by providing my own constructor — Upgrade
– Upgrade, Commented Feb 13, 2022 at 0:26
"Creative" alternative: struct S { std::array<int, 50> arr = []{ decltype(arr) rv; rv.fill(5); return rv; }(); }; — Ted Lyngmo
– Ted Lyngmo, Commented Feb 13, 2022 at 0:56

UnholySheep · Accepted Answer · 2022-02-13 00:30:05Z

Since a struct object needs to have its constructor called when being initialized you can just perform this assignment inside the constructor, e.g.:

struct S { int arr[50]; S() { for (int& val : arr) val = 5; } };

Or similarly you can use std::fill from the algorithm header

#include <algorithm> struct S { int arr[50]; S() { std::fill(std::begin(arr), std::end(arr), 5); } };

Yup - I believe std::fill() is exactly what the OP looking for :)

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