Defined in header <cstdio> int fflush( std::FILE* stream );
For output streams (and for update streams on which the last operation was output), writes any unwritten data from the stream's buffer to the associated output device.
For input streams (and for update streams on which the last operation was input), the behavior is undefined.
If stream is a null pointer, all open output streams are flushed, including the ones manipulated within library packages or otherwise not dir