Effects:
- Determine file_status s, as if by status(p) or status(p, ec), respectively.
- For the signature with argument ec, return false if an error occurred.
- Otherwise, if is_directory(s):
- Create a variable itr, as if by directory_iterator itr(p) ordirectory_iterator itr(p, ec), respectively.
- For the signature with argument ec, return false if an error occurred.
- Otherwise, return itr == directory_iterator().
- Otherwise:
- Determine uintmax_t sz, as if by file_size(p) or file_size(p, ec), respectively.
- For the signature with argument ec, return false if an error occurred.
- Otherwise, return sz == 0.