bool copy_file(const path& from, const path& to);
bool copy_file(const path& from, const path& to, error_code& ec) noexcept;
bool copy_file(const path& from, const path& to, copy_options options);
bool copy_file(const path& from, const path& to, copy_options options,
error_code& ec) noexcept;
(options & (copy_options::skip_existing | copy_options::overwrite_existing | copy_options::update_existing)) == copy_options::none