Sieve of Eratosthenes with C++ constexpr

prime.cpp

#include <stdio.h>

template <size_t N>
struct PrimeTable {
  constexpr PrimeTable() : sieve() {
    sieve[0] = sieve[1] = false;
    for (size_t i = 2; i < N; i++) sieve[i] = true;
    for (size_t i = 2; i < N; i++) {
      if (sieve[i])
        for (size_t j = i*i; j < N; j += i) sieve[j] = false;
    }
  }
  bool sieve[N];
};

int main() {
  constexpr auto table = PrimeTable<100000>();
  for (int i = 0; i < 20; i++) {
    printf("isPrime(%d): %d\n", i, table.sieve[i]);
  }
  return 0; 
}