basic_filebuf<charT,traits>* rdbuf() const;
Returns: const_cast<basic_filebuf<charT,traits>*>(&sb).
Returns: rdbuf()->is_open().
void open(const char* s,
ios_base::openmode mode = ios_base::in|ios_base::out);
Effects: Calls rdbuf()->open(s,mode). 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|ios_base::out);
Effects: calls open(s.c_str(), mode);
Effects: Calls rdbuf()->close() and, if that function returns returns a null pointer, calls setstate(failbit) ([iostate.flags]) (which may throw ios_base::failure).