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a1eaacb1 | 1 | '\" t |
fea681da MK |
2 | .\" Copyright (c) 1990, 1991 The Regents of the University of California. |
3 | .\" All rights reserved. | |
4 | .\" | |
5 | .\" This code is derived from software contributed to Berkeley by | |
6 | .\" Chris Torek and the American National Standards Committee X3, | |
7 | .\" on Information Processing Systems. | |
8 | .\" | |
47009d5e | 9 | .\" SPDX-License-Identifier: BSD-4-Clause-UC |
fea681da MK |
10 | .\" |
11 | .\" @(#)fflush.3 5.4 (Berkeley) 6/29/91 | |
12 | .\" | |
13 | .\" Converted for Linux, Mon Nov 29 15:22:01 1993, faith@cs.unc.edu | |
14 | .\" | |
e00c3a07 | 15 | .\" Modified 2000-07-22 by Nicolás Lichtmaier <nick@debian.org> |
fea681da MK |
16 | .\" Modified 2001-10-16 by John Levon <moz@compsoc.man.ac.uk> |
17 | .\" | |
4c1c5274 | 18 | .TH fflush 3 (date) "Linux man-pages (unreleased)" |
fea681da MK |
19 | .SH NAME |
20 | fflush \- flush a stream | |
afa8db94 AC |
21 | .SH LIBRARY |
22 | Standard C library | |
23 | .RI ( libc ", " \-lc ) | |
fea681da | 24 | .SH SYNOPSIS |
c7db92b9 | 25 | .nf |
fea681da | 26 | .B #include <stdio.h> |
68e4db0a | 27 | .PP |
cd03c9b8 | 28 | .BI "int fflush(FILE *_Nullable " stream ); |
c7db92b9 | 29 | .fi |
fea681da | 30 | .SH DESCRIPTION |
2b64c171 | 31 | For output streams, |
e511ffb6 | 32 | .BR fflush () |
fea681da MK |
33 | forces a write of all user-space buffered data for the given output or update |
34 | .I stream | |
c13182ef | 35 | via the stream's underlying write function. |
847e0d88 | 36 | .PP |
099263ce MK |
37 | For input streams associated with seekable files |
38 | (e.g., disk files, but not pipes or terminals), | |
2b64c171 MK |
39 | .BR fflush () |
40 | discards any buffered data that has been fetched from the underlying file, | |
20479b66 | 41 | but has not been consumed by the application. |
847e0d88 | 42 | .PP |
c13182ef | 43 | The open status of the stream is unaffected. |
fea681da MK |
44 | .PP |
45 | If the | |
46 | .I stream | |
8478ee02 | 47 | argument is NULL, |
e511ffb6 | 48 | .BR fflush () |
fea681da MK |
49 | flushes |
50 | .I all | |
51 | open output streams. | |
76033537 MK |
52 | .\" mtk: POSIX specifies that only output streams are flushed for this case. |
53 | .\" Also verified for glibc by experiment. | |
fea681da | 54 | .PP |
24b74457 | 55 | For a nonlocking counterpart, see |
fea681da | 56 | .BR unlocked_stdio (3). |
47297adb | 57 | .SH RETURN VALUE |
c13182ef MK |
58 | Upon successful completion 0 is returned. |
59 | Otherwise, | |
fea681da | 60 | .B EOF |
9e39c4da | 61 | is returned and |
fea681da MK |
62 | .I errno |
63 | is set to indicate the error. | |
64 | .SH ERRORS | |
65 | .TP | |
66 | .B EBADF | |
199431b6 | 67 | .I stream |
fea681da MK |
68 | is not an open stream, or is not open for writing. |
69 | .PP | |
70 | The function | |
e511ffb6 | 71 | .BR fflush () |
fea681da MK |
72 | may also fail and set |
73 | .I errno | |
9e39c4da | 74 | for any of the errors specified for |
fea681da | 75 | .BR write (2). |
676420f2 | 76 | .SH ATTRIBUTES |
0b8af3fa MK |
77 | For an explanation of the terms used in this section, see |
78 | .BR attributes (7). | |
79 | .TS | |
80 | allbox; | |
c466875e | 81 | lbx lb lb |
0b8af3fa MK |
82 | l l l. |
83 | Interface Attribute Value | |
84 | T{ | |
9e54434e BR |
85 | .na |
86 | .nh | |
676420f2 | 87 | .BR fflush () |
0b8af3fa MK |
88 | T} Thread safety MT-Safe |
89 | .TE | |
c466875e | 90 | .sp 1 |
3113c7f3 | 91 | .SH STANDARDS |
4131356c AC |
92 | C11, POSIX.1-2008. |
93 | .SH HISTORY | |
94 | C89, POSIX.1-2001, POSIX.1-2008. | |
847e0d88 | 95 | .PP |
6db34ce8 MK |
96 | POSIX.1-2001 did not specify the behavior for flushing of input streams, |
97 | but the behavior is specified in POSIX.1-2008. | |
fea681da MK |
98 | .SH NOTES |
99 | Note that | |
63aa9df0 | 100 | .BR fflush () |
1c709786 | 101 | flushes only the user-space buffers provided by the C library. |
fea681da | 102 | To ensure that the data is physically stored on disk |
75b94dc3 | 103 | the kernel buffers must be flushed too, for example, with |
fea681da MK |
104 | .BR sync (2) |
105 | or | |
106 | .BR fsync (2). | |
47297adb | 107 | .SH SEE ALSO |
fea681da MK |
108 | .BR fsync (2), |
109 | .BR sync (2), | |
110 | .BR write (2), | |
111 | .BR fclose (3), | |
f65efcf5 | 112 | .BR fileno (3), |
fea681da | 113 | .BR fopen (3), |
85a7ae73 | 114 | .BR fpurge (3), |
fea681da MK |
115 | .BR setbuf (3), |
116 | .BR unlocked_stdio (3) |