Section (3) fflush
fflush — flush a stream
For output streams,
forces a write of all user-space buffered data for the given
output or update
stream via the stream_zsingle_quotesz_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.
argument is NULL,
flushes all open
For a nonlocking counterpart, see unlocked_stdio(3).
Upon successful completion 0 is returned. Otherwise,
EOF is returned and
errno is set to indicate the
streamis not an open stream, or is not open for writing.
also fail and set
errno for any
of the errors specified for write(2).
For an explanation of the terms used in this section, see attributes(7).
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.
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).
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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.
Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions
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(#)fflush.3 5.4 (Berkeley) 6/29/91
Converted for Linux, Mon Nov 29 15:22:01 1993, faithcs.unc.edu
Modified 2000-07-22 by Nicolás Lichtmaier <nickdebian.org>
Modified 2001-10-16 by John Levon <mozcompsoc.man.ac.uk>