uintmax_t file_size(const path& p);
uintmax_t file_size(const path& p, error_code& ec) noexcept;
Returns: If !exists(p) || !is_regular_file(p) an error is reported ([fs.err.report]). Otherwise, the size in bytes of the file p resolves to, determined as if by the value of the POSIX stat structure member st_size obtained as if by POSIX stat(). The signature with argument ec returns static_cast<uintmax_t>(-1) if an error occurs.
Throws: As specified in [fs.err.report].