basic_filebuf<charT, traits>* rdbuf() const;

Returns: const_cast<basic_filebuf<charT, traits>*>(addressof(sb)).

native_handle_type native_handle() const noexcept;

Effects: Equivalent to: return rdbuf()->native_handle();

Returns: rdbuf()->is_open().

void open(const char* s, ios_base::openmode mode = ios_base::in); void open(const filesystem::path::value_type* s, ios_base::openmode mode = ios_base::in); // wide systems only; see [fstream.syn]

Effects: Calls rdbuf()->open(s, mode | ios_base​::​in).

If that function does not return a null pointer calls clear(), otherwise calls setstate(failbit) (which may throw ios_base​::​failure) ([iostate.flags]).

void open(const string& s, ios_base::openmode mode = ios_base::in); void open(const filesystem::path& s, ios_base::openmode mode = ios_base::in);

Effects: Calls open(s.c_str(), mode).

Effects: Calls rdbuf()->close() and, if that function returns a null pointer, calls setstate(failbit) (which may throw ios_base​::​failure) ([iostate.flags]).