redhat man page for fflush

FFLUSH(3)						     Linux Programmer's Manual							 FFLUSH(3)

NAME
       fflush - flush a stream

SYNOPSIS
       #include <stdio.h>

       int fflush(FILE *stream);

DESCRIPTION
       The  function fflush forces a write of all user-space buffered data for the given output or update stream via the stream's underlying write
       function.  The open status of the stream is unaffected.

       If the stream argument is NULL, fflush flushes all open output streams.

       For a non-locking counterpart, see unlocked_stdio(3).

RETURN VALUE
       Upon successful completion 0 is returned.  Otherwise, EOF is returned and the global variable errno is set to indicate the error.

ERRORS
       EBADF  Stream is not an open stream, or is not open for writing.

       The function fflush may also fail and set errno for any of the errors specified for the routine write(2).

NOTES
       Note that fflush() only flushes the user space buffers provided by the C library.  To ensure that the data is physically stored on disk the
       kernel buffers must be flushed too, e.g. with sync(2) or fsync(2).

CONFORMING TO
       The function fflush() conforms to ANSI X3.159-1989 (``ANSI C'').

SEE ALSO
       fsync(2), sync(2), write(2), fclose(3), fopen(3), setbuf(3), unlocked_stdio(3)

BSD MANPAGE
							    1993-11-29								 FFLUSH(3)