For output streams, fflush()
forces a write of all user-space buffered data for the given
output or update stream via the stream's
underlying write function.
For input streams associated with seekable files (e.g.,
disk files, but not pipes or terminals), 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.
If the stream
argument is NULL, fflush()
flushes all open
output streams.
Upon successful completion 0 is returned. Otherwise,
EOF is returned and
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 write(2).
ATTRIBUTES
For an explanation of the terms used in this section, see
attributes(7).
Interface
Attribute
Value
fflush()
Thread safety
MT-Safe
CONFORMING TO
C89, C99, POSIX.1-2001, POSIX.1-2008.
POSIX.1-2001 did not specify the behavior for flushing of
input streams, but the behavior is specified in
POSIX.1-2008.
NOTES
Note that 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 sync(2) or fsync(2).
This page is part of release 4.07 of the Linux 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/.
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.
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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>