Initialize an array in a struct

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, Feb 13 '22 at 00:20
Can you please give me an example how is it possible by providing my own constructor — Upgrade, Feb 13 '22 at 00:26
"Creative" alternative: `struct S { std::array arr = []{ decltype(arr) rv; rv.fill(5); return rv; }(); };` — Ted Lyngmo, Feb 13 '22 at 00:56

score 2 · Accepted Answer · answered Feb 13 '22 at 00:30

2

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);
  }
};

answered Feb 13 '22 at 00:30

UnholySheep

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Yup - I believe [std::fill()](https://en.cppreference.com/w/cpp/algorithm/fill) is exactly what the OP looking for :) – paulsm4 Feb 13 '22 at 00:31

Initialize an array in a struct

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