| .\" 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. |
| .\" |
| .\" %%%LICENSE_START(BSD_4_CLAUSE_UCB) |
| .\" Redistribution and use in source and binary forms, with or without |
| .\" modification, are permitted provided that the following conditions |
| .\" are met: |
| .\" 1. Redistributions of source code must retain the above copyright |
| .\" notice, this list of conditions and the following disclaimer. |
| .\" 2. Redistributions in binary form must reproduce the above copyright |
| .\" notice, this list of conditions and the following disclaimer in the |
| .\" documentation and/or other materials provided with the distribution. |
| .\" 3. All advertising materials mentioning features or use of this software |
| .\" must display the following acknowledgement: |
| .\" This product includes software developed by the University of |
| .\" California, Berkeley and its contributors. |
| .\" 4. Neither the name of the University nor the names of its contributors |
| .\" may be used to endorse or promote products derived from this software |
| .\" without specific prior written permission. |
| .\" |
| .\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND |
| .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE |
| .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE |
| .\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE |
| .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL |
| .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS |
| .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) |
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| .\" %%%LICENSE_END |
| .\" |
| .\" @(#)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 Nicolรกs Lichtmaier <nick@debian.org> |
| .\" Modified 2001-10-16 by John Levon <moz@compsoc.man.ac.uk> |
| .\" |
| .TH FFLUSH 3 2017-09-15 "GNU" "Linux Programmer's Manual" |
| .SH NAME |
| fflush \- flush a stream |
| .SH SYNOPSIS |
| .B #include <stdio.h> |
| .PP |
| .BI "int fflush(FILE *" stream ); |
| .SH DESCRIPTION |
| For output streams, |
| .BR fflush () |
| forces a write of all user-space buffered data for the given output or update |
| .I stream |
| via the stream's underlying write function. |
| .PP |
| For input streams associated with seekable files |
| (e.g., disk files, but not pipes or terminals), |
| .BR fflush () |
| discards any buffered data that has been fetched from the underlying file, |
| but has not been consumed by the application. |
| .PP |
| The open status of the stream is unaffected. |
| .PP |
| If the |
| .I stream |
| argument is NULL, |
| .BR fflush () |
| flushes |
| .I all |
| open output streams. |
| .\" mtk: POSIX specifies that only output streams are flushed for this case. |
| .\" Also verified for glibc by experiment. |
| .PP |
| For a nonlocking counterpart, see |
| .BR unlocked_stdio (3). |
| .SH RETURN VALUE |
| Upon successful completion 0 is returned. |
| Otherwise, |
| .B EOF |
| is returned and |
| .I errno |
| is set to indicate the error. |
| .SH ERRORS |
| .TP |
| .B EBADF |
| .I stream |
| is not an open stream, or is not open for writing. |
| .PP |
| The function |
| .BR fflush () |
| may also fail and set |
| .I errno |
| for any of the errors specified for |
| .BR write (2). |
| .SH ATTRIBUTES |
| For an explanation of the terms used in this section, see |
| .BR attributes (7). |
| .TS |
| allbox; |
| lb lb lb |
| l l l. |
| Interface Attribute Value |
| T{ |
| .BR fflush () |
| T} Thread safety MT-Safe |
| .TE |
| .SH CONFORMING TO |
| C89, C99, POSIX.1-2001, POSIX.1-2008. |
| .PP |
| POSIX.1-2001 did not specify the behavior for flushing of input streams, |
| but the behavior is specified in POSIX.1-2008. |
| .SH NOTES |
| Note that |
| .BR 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 |
| .BR sync (2) |
| or |
| .BR fsync (2). |
| .SH SEE ALSO |
| .BR fsync (2), |
| .BR sync (2), |
| .BR write (2), |
| .BR fclose (3), |
| .BR fileno (3), |
| .BR fopen (3), |
| .BR setbuf (3), |
| .BR unlocked_stdio (3) |