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1 | .\" Copyright (c) 1990, 1991 The Regents of the University of California. |
2 | .\" All rights reserved. | |
3 | .\" | |
4 | .\" This code is derived from software contributed to Berkeley by | |
5 | .\" Chris Torek and the American National Standards Committee X3, | |
6 | .\" on Information Processing Systems. | |
7 | .\" | |
a9cd9cb7 | 8 | .\" %%%LICENSE_START(BSD_4_CLAUSE_UCB) |
fea681da MK |
9 | .\" Redistribution and use in source and binary forms, with or without |
10 | .\" modification, are permitted provided that the following conditions | |
11 | .\" are met: | |
12 | .\" 1. Redistributions of source code must retain the above copyright | |
13 | .\" notice, this list of conditions and the following disclaimer. | |
14 | .\" 2. Redistributions in binary form must reproduce the above copyright | |
15 | .\" notice, this list of conditions and the following disclaimer in the | |
16 | .\" documentation and/or other materials provided with the distribution. | |
17 | .\" 3. All advertising materials mentioning features or use of this software | |
18 | .\" must display the following acknowledgement: | |
19 | .\" This product includes software developed by the University of | |
20 | .\" California, Berkeley and its contributors. | |
21 | .\" 4. Neither the name of the University nor the names of its contributors | |
22 | .\" may be used to endorse or promote products derived from this software | |
23 | .\" without specific prior written permission. | |
24 | .\" | |
25 | .\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND | |
26 | .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE | |
27 | .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE | |
28 | .\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE | |
29 | .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL | |
30 | .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS | |
31 | .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) | |
32 | .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT | |
33 | .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY | |
34 | .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF | |
35 | .\" SUCH DAMAGE. | |
8c9302dc | 36 | .\" %%%LICENSE_END |
fea681da MK |
37 | .\" |
38 | .\" @(#)fflush.3 5.4 (Berkeley) 6/29/91 | |
39 | .\" | |
40 | .\" Converted for Linux, Mon Nov 29 15:22:01 1993, faith@cs.unc.edu | |
41 | .\" | |
e00c3a07 | 42 | .\" Modified 2000-07-22 by Nicolás Lichtmaier <nick@debian.org> |
fea681da MK |
43 | .\" Modified 2001-10-16 by John Levon <moz@compsoc.man.ac.uk> |
44 | .\" | |
4b8c67d9 | 45 | .TH FFLUSH 3 2017-09-15 "GNU" "Linux Programmer's Manual" |
fea681da MK |
46 | .SH NAME |
47 | fflush \- flush a stream | |
48 | .SH SYNOPSIS | |
49 | .B #include <stdio.h> | |
68e4db0a | 50 | .PP |
fea681da MK |
51 | .BI "int fflush(FILE *" stream ); |
52 | .SH DESCRIPTION | |
2b64c171 | 53 | For output streams, |
e511ffb6 | 54 | .BR fflush () |
fea681da MK |
55 | forces a write of all user-space buffered data for the given output or update |
56 | .I stream | |
c13182ef | 57 | via the stream's underlying write function. |
847e0d88 | 58 | .PP |
099263ce MK |
59 | For input streams associated with seekable files |
60 | (e.g., disk files, but not pipes or terminals), | |
2b64c171 MK |
61 | .BR fflush () |
62 | discards any buffered data that has been fetched from the underlying file, | |
20479b66 | 63 | but has not been consumed by the application. |
847e0d88 | 64 | .PP |
c13182ef | 65 | The open status of the stream is unaffected. |
fea681da MK |
66 | .PP |
67 | If the | |
68 | .I stream | |
8478ee02 | 69 | argument is NULL, |
e511ffb6 | 70 | .BR fflush () |
fea681da MK |
71 | flushes |
72 | .I all | |
73 | open output streams. | |
76033537 MK |
74 | .\" mtk: POSIX specifies that only output streams are flushed for this case. |
75 | .\" Also verified for glibc by experiment. | |
fea681da | 76 | .PP |
24b74457 | 77 | For a nonlocking counterpart, see |
fea681da | 78 | .BR unlocked_stdio (3). |
47297adb | 79 | .SH RETURN VALUE |
c13182ef MK |
80 | Upon successful completion 0 is returned. |
81 | Otherwise, | |
fea681da | 82 | .B EOF |
9e39c4da | 83 | is returned and |
fea681da MK |
84 | .I errno |
85 | is set to indicate the error. | |
86 | .SH ERRORS | |
87 | .TP | |
88 | .B EBADF | |
199431b6 | 89 | .I stream |
fea681da MK |
90 | is not an open stream, or is not open for writing. |
91 | .PP | |
92 | The function | |
e511ffb6 | 93 | .BR fflush () |
fea681da MK |
94 | may also fail and set |
95 | .I errno | |
9e39c4da | 96 | for any of the errors specified for |
fea681da | 97 | .BR write (2). |
676420f2 | 98 | .SH ATTRIBUTES |
0b8af3fa MK |
99 | For an explanation of the terms used in this section, see |
100 | .BR attributes (7). | |
101 | .TS | |
102 | allbox; | |
103 | lb lb lb | |
104 | l l l. | |
105 | Interface Attribute Value | |
106 | T{ | |
676420f2 | 107 | .BR fflush () |
0b8af3fa MK |
108 | T} Thread safety MT-Safe |
109 | .TE | |
47297adb | 110 | .SH CONFORMING TO |
2b64c171 | 111 | C89, C99, POSIX.1-2001, POSIX.1-2008. |
847e0d88 | 112 | .PP |
6db34ce8 MK |
113 | POSIX.1-2001 did not specify the behavior for flushing of input streams, |
114 | but the behavior is specified in POSIX.1-2008. | |
fea681da MK |
115 | .SH NOTES |
116 | Note that | |
63aa9df0 | 117 | .BR fflush () |
1c709786 | 118 | flushes only the user-space buffers provided by the C library. |
fea681da | 119 | To ensure that the data is physically stored on disk |
75b94dc3 | 120 | the kernel buffers must be flushed too, for example, with |
fea681da MK |
121 | .BR sync (2) |
122 | or | |
123 | .BR fsync (2). | |
47297adb | 124 | .SH SEE ALSO |
fea681da MK |
125 | .BR fsync (2), |
126 | .BR sync (2), | |
127 | .BR write (2), | |
128 | .BR fclose (3), | |
f65efcf5 | 129 | .BR fileno (3), |
fea681da MK |
130 | .BR fopen (3), |
131 | .BR setbuf (3), | |
132 | .BR unlocked_stdio (3) |