Description

   The output files are normally buffered only if they are not
   directed to a terminal, except for stderr, which is not buffered
   by default.

   The fflush function flushes the C RTL buffers. However,
   RMS has its own buffers. The fflush function does not guarantee
   that the file will be written to disk. (See the description of
   fsync for a way to flush buffers to disk.)

   If the file pointed to by file_ptr was opened in record mode
   and if there is unwritten data in the buffer, then fflush always
   generates a record.