1.\" Copyright (c) 1990, 1991, 1993 2.\" The Regents of the University of California. 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.\" 8.\" Redistribution and use in source and binary forms, with or without 9.\" modification, are permitted provided that the following conditions 10.\" are met: 11.\" 1. Redistributions of source code must retain the above copyright 12.\" notice, this list of conditions and the following disclaimer. 13.\" 2. Redistributions in binary form must reproduce the above copyright 14.\" notice, this list of conditions and the following disclaimer in the 15.\" documentation and/or other materials provided with the distribution. 16.\" 3. Neither the name of the University nor the names of its contributors 17.\" may be used to endorse or promote products derived from this software 18.\" without specific prior written permission. 19.\" 20.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 21.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 22.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 23.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 24.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 25.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 26.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 27.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 28.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 29.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 30.\" SUCH DAMAGE. 31.\" 32.\" @(#)fflush.3 8.1 (Berkeley) 6/4/93 33.\" $FreeBSD: src/lib/libc/stdio/fflush.3,v 1.11 2007/01/09 00:28:06 imp Exp $ 34.\" 35.Dd November 22, 2020 36.Dt FFLUSH 3 37.Os 38.Sh NAME 39.Nm fflush , 40.Nm fflush_unlocked , 41.Nm fpurge 42.Nd flush a stream 43.Sh LIBRARY 44.Lb libc 45.Sh SYNOPSIS 46.In stdio.h 47.Ft int 48.Fn fflush "FILE *stream" 49.Ft int 50.Fn fflush_unlocked "FILE *stream" 51.Ft int 52.Fn fpurge "FILE *stream" 53.Sh DESCRIPTION 54The function 55.Fn fflush 56forces a write of all buffered data for the given output or update 57.Fa stream 58via the stream's underlying write function. 59The open status of the stream is unaffected. 60.Pp 61If the 62.Fa stream 63argument is 64.Dv NULL , 65.Fn fflush 66flushes 67.Em all 68open output streams. 69.Pp 70The 71.Fn fflush_unlocked 72function is equivalent to 73.Fn fflush , 74except that the caller is responsible for locking the stream with 75.Xr flockfile 3 76before calling it. 77This function may be used to avoid the overhead of locking the stream and to 78prevent races when multiple threads are operating on the same stream. 79.Pp 80The function 81.Fn fpurge 82erases any input or output buffered in the given 83.Fa stream . 84For output streams this discards any unwritten output. 85For input streams this discards any input read from the underlying object 86but not yet obtained via 87.Xr getc 3 ; 88this includes any text pushed back via 89.Xr ungetc 3 . 90.Sh RETURN VALUES 91Upon successful completion 0 is returned. 92Otherwise, 93.Dv EOF 94is returned and the global variable 95.Va errno 96is set to indicate the error. 97.Sh ERRORS 98.Bl -tag -width Er 99.It Bq Er EBADF 100The 101.Fa stream 102argument 103is not an open stream. 104.El 105.Pp 106The function 107.Fn fflush 108may also fail and set 109.Va errno 110for any of the errors specified for the routine 111.Xr write 2 , 112except that in case of 113.Fa stream 114being a read-only descriptor, 115.Fn fflush 116returns 0. 117.Sh SEE ALSO 118.Xr write 2 , 119.Xr fclose 3 , 120.Xr fopen 3 , 121.Xr setbuf 3 122.Sh STANDARDS 123The 124.Fn fflush 125function 126conforms to 127.St -isoC . 128