Filling an array during compilation

Asked Jan 30 '16 at 12:31

Active Jan 30 '16 at 12:39

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I am trying to fill a char array using another constexpr char array during compile time, but I do not see how could I do this.

I am trying to emulate the following:

constexpr char arr1[N] = {/* Permutation of the numbers 0..N-1 */}
char arr2[N];
for(int i=0;i<N;++i)
    arr2[arr1[i]]=i;

but since I cannot return an array from a function, I do not know how to do this. Furthermore, I would like arr2 to be constexpr, since everything I need to compute it is known at compile time.

Any ideas about how to do this?

edited Jan 30 '16 at 12:39

πάντα ῥεῖ

asked Jan 30 '16 at 12:31

Lezkus

I'm not sure, but maybe a variadic template struct or function could help to generate some initializer list. – πάντα ῥεῖ Jan 30 '16 at 12:34
std::array has some limitations when it comes to constexpr, but yeah a simple struct could help you out. – melak47 Jan 30 '16 at 12:34
I didn't use std::array in favor of regular arrays because of the problems it has with constexpr brackets operators and so. Anyways, I do not think this would be any simpler using std::array, would it? – Lezkus Jan 30 '16 at 12:36
@GuillaumeGris Of course, that does the trick! – πάντα ῥεῖ Jan 30 '16 at 12:36
@Lezkus `std::array` allows some tricks, that you would need to implement yourself dealing with raw (regular) arrays. – πάντα ῥεῖ Jan 30 '16 at 12:38
@GuillaumeGris I already read that post, but I do not know how could I apply that to this problem, since I'm working with the index of the array here. I'm sorry, I'm new to TMP. If you could provide a sample code it would be very appreciated. – Lezkus Jan 30 '16 at 12:38
Try [this](http://coliru.stacked-crooked.com/a/6084dc05b3c9289e)? – melak47 Jan 30 '16 at 12:40
@Lezkus Mind to read the info popping up when tagging please. – πάντα ῥεῖ Jan 30 '16 at 12:40

Filling an array during compilation

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