How Can I Create a Constexpr Array of N Elements in C 11?

Creating a Constexpr Array of N Elements in C 11

In C 11, creating a constexpr array of N elements is not as straightforward as in later versions of the language. While constexpr arrays were introduced in C 11, their functionality was limited, and it is not possible to create constexpr arrays of variable length using the same syntax as in C 14 and beyond.

However, using some advanced techniques and constexpr functions, it is possible to achieve similar results in C 11. Here's how:

#include <iostream>

template<int N>
struct A {
    constexpr A() : arr() {
        for (auto i = 0; i != N; ++i)
            arr[i] = i; 
    }
    int arr[N];
};

int main() {
    constexpr auto a = A<4>();
    for (auto x : a.arr)
        std::cout << x << '\n';
}

In this example, we define a constexpr function A that initializes an array of length N with the values 0 to N-1. The function is declared as constexpr to ensure that its execution time is known at compile-time.

In the main function, we create an instance of A<4> and print the values of the array. Since the array is constexpr, the compiler can determine its values at compile-time, ensuring that no runtime computations are performed for the array.

This approach allows us to create constexpr arrays in C 11, even though the syntax is more complex than in later versions of the language.

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