Const array initialization if its too long

Question

In my answer to this question it was mentioned that the code I posted wouldn't work if the variable was declared as const.

What if i want to initialize a long array that's const type

int main (){
    const int ar[100];
 //this is invalid in c++
 //something like this

    for (int i=0;i <100;++i)
        ar[i]=i;
    return 0;
}

Are there other ways to do this than using the #define method proposed in that question?

@CoryKramer I think he's saying that he can't modify a const int[] after definition, therefore he can't initialize it. — KABoissonneault, Jun 10 '15 at 13:47
`const int ar[100];` is not even legal C++, you cannot leave the array un-initialized — vsoftco, Jun 10 '15 at 13:50
I suppose this is a follow-up question to my comment to [this answer](http://stackoverflow.com/a/30756798/584518)? In that case, simply check the answer posted by yours sincerely to that question. — Lundin, Jun 10 '15 at 13:57
After declaring a const variable, you can no longer change its values. You should assign the values when you instantiate the object or variable. — Ediac, Jun 10 '15 at 13:58
@Lundin exactly, but i dont find proper ans there.... if u dont mind kindly guide me — Sagar Kar, Jun 10 '15 at 14:28
@SagarKar What part of [my answer](http://stackoverflow.com/a/30757138/584518) didn't you understand? It is universal and applies to any data type, not just chars. — Lundin, Jun 10 '15 at 14:30
@Lundin ow u said about that #define method.... i mentioned that i am looking for something other than that... thats a cool method indeed — Sagar Kar, Jun 10 '15 at 14:33
There is no standard way to do so. [Here is a very similar question](http://stackoverflow.com/questions/21528288/c-structure-array-initializing) with a very similar answer by me, plus some answers suggesting non-standard gcc extensions. — Lundin, Jun 10 '15 at 14:35
Thanks man! Nxt time i will try to post more meaningful question that dont go for downvote! @Lundin — Sagar Kar, Jun 10 '15 at 14:39
This isn't a bad question, it is just very hard to understand for others what you mean, since you are referring to that other question, without posting a link to it. So nobody except me understood what you were asking :) — Lundin, Jun 10 '15 at 14:46
you could also use templates: http://stackoverflow.com/questions/6060103/create-static-array-with-variadic-templates — m.s., Jun 10 '15 at 15:18

score 2 · Accepted Answer · answered Jun 10 '15 at 15:14

There's no way to do it directly, without hacks.

In C++ one way to work around this problem is to take advantage of the fact that inside their constructors const objects are still modifiable. So, you can wrap your array into a class and initialize it in the constructor

struct Arr 
{
  int a[100];

  A() 
  {
    for (unsigned i = 0; i < 100; ++i)
      a[i] = i;
  }
};

and then just declare

const Arr arr;

Of course, now you will have to access it as arr.a[i], unless you override the operators in Arr.

score 1 · Answer 2 · answered Jun 10 '15 at 14:56

1

You could use a trick... initialize a regular array and then get a reference to a const array:

int arr[100];
for (int i=0; i<100; i++) arr[i] = i*i;

const int (&carr)[100] = arr;

answered Jun 10 '15 at 14:56

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Cool thats somewhag cheating lol.... nice way though – Sagar Kar Jun 10 '15 at 15:04

Const array initialization if its too long

2 Answers2