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.\" This code is derived from software contributed to Berkeley by
.\" Chris Torek and the American National Standards Committee X3,
.\" on Information Processing Systems.
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.\"     @(#)fflush.3	5.4 (Berkeley) 6/29/91
.\"
.\" Converted for Linux, Mon Nov 29 15:22:01 1993, faith@cs.unc.edu
.\"
.\" Modified 2000-07-22 by Nicolás Lichtmaier <nick@debian.org>
.\" Modified 2001-10-16 by John Levon <moz@compsoc.man.ac.uk>
.\"
.TH FFLUSH 3  2009-09-06 "GNU" "Linux Programmer's Manual"
.SH NAME
fflush \- flush a stream
.SH SYNOPSIS
.B #include <stdio.h>
.sp
.BI "int fflush(FILE *" stream );
.SH DESCRIPTION
For output streams,
.BR fflush ()
forces a write of all user-space buffered data for the given output or update
.I stream
via the stream's underlying write function.
For input streams,
.BR fflush ()
discards any buffered data that has been fetched from the underlying file,
but has not been consumed by the application.
The open status of the stream is unaffected.
.PP
If the
.I stream
argument is NULL,
.BR fflush ()
flushes
.I all
open output streams.
.PP
For a nonlocking counterpart, see
.BR unlocked_stdio (3).
.SH "RETURN VALUE"
Upon successful completion 0 is returned.
Otherwise,
.B EOF
is returned and
.I errno
is set to indicate the error.
.SH ERRORS
.TP
.B EBADF
.I Stream
is not an open stream, or is not open for writing.
.PP
The function
.BR fflush ()
may also fail and set
.I errno
for any of the errors specified for
.BR write (2).
.SH "CONFORMING TO"
C89, C99, POSIX.1-2001, POSIX.1-2008.

The standards do not specify the behavior for input streams.
Most other implementations behave the same as Linux.
.\" Verified on: Solaris 8.
.SH NOTES
Note that
.BR 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, for example, with
.BR sync (2)
or
.BR fsync (2).
.SH "SEE ALSO"
.BR fsync (2),
.BR sync (2),
.BR write (2),
.BR fclose (3),
.BR fopen (3),
.BR setbuf (3),
.BR unlocked_stdio (3)
.SH COLOPHON
This page is part of release 3.44 of the Linux
.I man-pages
project.
A description of the project,
and information about reporting bugs,
can be found at
http://www.kernel.org/doc/man-pages/.