PreamblePostamble-take1.cpp

void PrePost(const std::function<void(void)>& f) {
  std::cout << "pre\n";
  f();
  std::cout << "post\n";
}

int main() {   
  double a = 1.1;
  double b = 2.2;
  double c = 3.3;
  PrePost(
    [&a, &b, &c](){ 
      std::cout << a << " " << b << " " << c << "\n"; 
    }
  );
}