Initialize a const array in compile time with a template-based length

Question

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Programmatically create static arrays at compile time in C++

Is it possible to initialize the following array in compile time?

template<int n> void
foo()
{
    static int pairs[2*n]; // = {0,0, 1,1, ..., n-1,n-1}
    for (int i = 0; i < n; i++)
    {
         pairs[2*i] = pairs[2*i+1] = i;
    }

    do_something_with_pairs(pairs);
}

(I use Clang on Xcode 4.5 so C++11 is OK)

the loop uses indices beyond the end of the array => **Undefined Behavior**. — Cheers and hth. - Alf, Nov 29 '12 at 11:42
I'm wondering how many people have put their work aside and trying hard to solve this. This is a very good question. But I'm giving up. — , Nov 29 '12 at 11:50

score 0 · Answer 1 · answered Nov 29 '12 at 11:49

As far as I know it's not possible to extend an array initializer, and that rules out a recursive template based solution as a means to generate static initialization data.

However, you can do the simple thing of having a static array with as many data points as you will ever use. This can be generated by a simple script. Or e.g. by the Boost preprocessor library.

Then you can just use a pointer to that array.

Initialize a const array in compile time with a template-based length

1 Answers1