mirror of https://github.com/mkerrisk/man-pages
133 lines
4.2 KiB
Groff
133 lines
4.2 KiB
Groff
.\" Copyright (c) 1990, 1991 The Regents of the University of California.
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.\" All rights reserved.
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.\"
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.\" This code is derived from software contributed to Berkeley by
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.\" Chris Torek and the American National Standards Committee X3,
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.\" on Information Processing Systems.
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.\"
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.\" %%%LICENSE_START(BSD_4_CLAUSE_UCB)
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed by the University of
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.\" California, Berkeley and its contributors.
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.\" 4. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\" %%%LICENSE_END
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.\"
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.\" @(#)fflush.3 5.4 (Berkeley) 6/29/91
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.\"
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.\" Converted for Linux, Mon Nov 29 15:22:01 1993, faith@cs.unc.edu
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.\"
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.\" Modified 2000-07-22 by Nicolás Lichtmaier <nick@debian.org>
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.\" Modified 2001-10-16 by John Levon <moz@compsoc.man.ac.uk>
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.\"
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.TH FFLUSH 3 2017-09-15 "GNU" "Linux Programmer's Manual"
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.SH NAME
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fflush \- flush a stream
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.SH SYNOPSIS
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.B #include <stdio.h>
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.PP
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.BI "int fflush(FILE *" stream );
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.SH DESCRIPTION
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For output streams,
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.BR fflush ()
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forces a write of all user-space buffered data for the given output or update
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.I stream
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via the stream's underlying write function.
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.PP
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For input streams associated with seekable files
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(e.g., disk files, but not pipes or terminals),
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.BR fflush ()
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discards any buffered data that has been fetched from the underlying file,
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but has not been consumed by the application.
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.PP
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The open status of the stream is unaffected.
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.PP
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If the
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.I stream
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argument is NULL,
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.BR fflush ()
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flushes
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.I all
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open output streams.
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.\" mtk: POSIX specifies that only output streams are flushed for this case.
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.\" Also verified for glibc by experiment.
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.PP
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For a nonlocking counterpart, see
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.BR unlocked_stdio (3).
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.SH RETURN VALUE
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Upon successful completion 0 is returned.
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Otherwise,
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.B EOF
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is returned and
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.I errno
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is set to indicate the error.
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.SH ERRORS
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.TP
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.B EBADF
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.I stream
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is not an open stream, or is not open for writing.
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.PP
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The function
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.BR fflush ()
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may also fail and set
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.I errno
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for any of the errors specified for
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.BR write (2).
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.SH ATTRIBUTES
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For an explanation of the terms used in this section, see
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.BR attributes (7).
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.TS
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allbox;
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lb lb lb
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l l l.
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Interface Attribute Value
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T{
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.BR fflush ()
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T} Thread safety MT-Safe
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.TE
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.SH CONFORMING TO
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C89, C99, POSIX.1-2001, POSIX.1-2008.
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.PP
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POSIX.1-2001 did not specify the behavior for flushing of input streams,
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but the behavior is specified in POSIX.1-2008.
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.SH NOTES
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Note that
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.BR fflush ()
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flushes only the user-space buffers provided by the C library.
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To ensure that the data is physically stored on disk
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the kernel buffers must be flushed too, for example, with
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.BR sync (2)
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or
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.BR fsync (2).
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.SH SEE ALSO
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.BR fsync (2),
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.BR sync (2),
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.BR write (2),
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.BR fclose (3),
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.BR fileno (3),
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.BR fopen (3),
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.BR setbuf (3),
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.BR unlocked_stdio (3)
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