Convert a compile-time constant to a char-array containing the binary representation.

to_bin.cpp

#include <iostream>

template <unsigned long long N, char... C>
constexpr auto to_bin = to_bin<(N >> 1), '0' + (N & 1), C...>;

template <char... C>
constexpr char to_bin<0, C...>[] = { C..., '\0' };


template <unsigned long long N, size_t L, char... C>
constexpr auto to_bin_fixed = to_bin_fixed<(N >> 1), L - 1, '0' + (N & 1), C...>;

template <unsigned long long N, char... C>
constexpr char to_bin_fixed<N, 0, C...>[] = { C..., '\0' };

int main() {
    std::cout << to_bin<42> << "\n";
    // => "101010"

    std::cout << to_bin_fixed<42, 8> << "\n";
    // => "00101010"
}