.\" Copyright (c) 1990, 1991 The Regents of the University of California.

.\" All rights reserved.

.\"

.\" This code is derived from software contributed to Berkeley by

.\" Chris Torek and the American National Standards Committee X3,

.\" on Information Processing Systems.

.\"

.\" %%%LICENSE_START(BSD_4_CLAUSE_UCB)

.\" Redistribution and use in source and binary forms, with or without

.\" modification, are permitted provided that the following conditions

.\" are met:

.\" 1. Redistributions of source code must retain the above copyright

.\"    notice, this list of conditions and the following disclaimer.

.\" 2. Redistributions in binary form must reproduce the above copyright

.\"    notice, this list of conditions and the following disclaimer in the

.\"    documentation and/or other materials provided with the distribution.

.\" 3. All advertising materials mentioning features or use of this software

.\"    must display the following acknowledgement:

.\"	This product includes software developed by the University of

.\"	California, Berkeley and its contributors.

.\" 4. Neither the name of the University nor the names of its contributors

.\"    may be used to endorse or promote products derived from this software

.\"    without specific prior written permission.

.\"

.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND

.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE

.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE

.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE

.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL

.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS

.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)

.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT

.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY

.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF

.\" SUCH DAMAGE.

.\" %%%LICENSE_END

.\"

.\"     @(#)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  2017-09-15 "GNU" "Linux Programmer's Manual"

.SH NAME

fflush \- flush a stream

.SH SYNOPSIS

.B #include <stdio.h>

.PP

.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.

.PP

For input streams associated with seekable files

(e.g., disk files, but not pipes or terminals),

.BR fflush ()

discards any buffered data that has been fetched from the underlying file,

but has not been consumed by the application.

.PP

The open status of the stream is unaffected.

.PP

If the

.I stream

argument is NULL,

.BR fflush ()

flushes

.I all

open output streams.

.\" mtk: POSIX specifies that only output streams are flushed for this case.

.\" Also verified for glibc by experiment.

.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 ATTRIBUTES

For an explanation of the terms used in this section, see

.BR attributes (7).

.TS

allbox;

lb lb lb

l l l.

Interface	Attribute	Value

T{

.BR fflush ()

T}	Thread safety	MT-Safe

.TE

.SH CONFORMING TO

C89, C99, POSIX.1-2001, POSIX.1-2008.

.PP

POSIX.1-2001 did not specify the behavior for flushing of input streams,

but the behavior is specified in POSIX.1-2008.

.SH NOTES

Note that

.BR fflush ()

flushes only 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 fileno (3),

.BR fopen (3),

.BR setbuf (3),

.BR unlocked_stdio (3)

.SH COLOPHON

This page is part of release 4.15 of the Linux

.I man-pages

project.

A description of the project,

information about reporting bugs,

and the latest version of this page,

can be found at

\%https://www.kernel.org/doc/man\-pages/.