fill vector with random elements

Why my lambda doesn't put elements in vector?

void generate_N_numbers_in_the_vector(std::vector<int> &vec, int &M,
                                      const int &N) {
  std::random_device rand;
  static std::mt19937 gen(rand());
  static std::uniform_int_distribution<int> distribution(0, M);
  vec.reserve(N);

  std::generate(vec.begin(), vec.end(), []() { return distribution(gen); });

  for (auto elem : vec) std::cout << elem << std::endl;
}