I'm reading a code from here:
<https://github.com/chenshuo/muduo/blob/master/muduo/base/Date.cc>

But I'm confused about these two lines:

```
char require_32_bit_integer_at_least[sizeof(int) >= sizeof(int32_t) ? 1 : -1];

```

and

```
(void) require_32_bit_integer_at_least; // no warning please

```

What's the purpose of them?

```
char require_32_bit_integer_at_least[sizeof(int) >= sizeof(int32_t) ? 1 : -1];

int getJulianDayNumber(int year, int month, int day)
{
  (void) require_32_bit_integer_at_least; // no warning please
  int a = (14 - month) / 12;
  int y = year + 4800 - a;
  int m = month + 12 * a - 3;
  return day + (153*m + 2) / 5 + y*365 + y/4 - y/100 + y/400 - 32045;
}

```