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.Dd May 1, 2020 33.Dt FFLUSH 3 34.Os 35.Sh NAME 36.Nm fflush , 37.Nm fflush_unlocked , 38.Nm fpurge 39.Nd flush a stream 40.Sh LIBRARY 41.Lb libc 42.Sh SYNOPSIS 43.In stdio.h 44.Ft int 45.Fn fflush "FILE *stream" 46.Ft int 47.Fn fflush_unlocked "FILE *stream" 48.Ft int 49.Fn fpurge "FILE *stream" 50.Sh DESCRIPTION 51The function 52.Fn fflush 53forces a write of all buffered data for the given output or update 54.Fa stream 55via the stream's underlying write function. 56The open status of the stream is unaffected. 57.Pp 58If the 59.Fa stream 60argument is 61.Dv NULL , 62.Fn fflush 63flushes 64.Em all 65open output streams. 66.Pp 67The 68.Fn fflush_unlocked 69function is equivalent to 70.Fn fflush , 71except that the caller is responsible for locking the stream with 72.Xr flockfile 3 73before calling it. 74This function may be used to avoid the overhead of locking the stream and to 75prevent races when multiple threads are operating on the same stream. 76.Pp 77The function 78.Fn fpurge 79erases any input or output buffered in the given 80.Fa stream . 81For output streams this discards any unwritten output. 82For input streams this discards any input read from the underlying object 83but not yet obtained via 84.Xr getc 3 ; 85this includes any text pushed back via 86.Xr ungetc 3 . 87.Sh RETURN VALUES 88Upon successful completion 0 is returned. 89Otherwise, 90.Dv EOF 91is returned and the global variable 92.Va errno 93is set to indicate the error. 94.Sh ERRORS 95.Bl -tag -width Er 96.It Bq Er EBADF 97The 98.Fa stream 99argument 100is not an open stream. 101.El 102.Pp 103The function 104.Fn fflush 105may also fail and set 106.Va errno 107for any of the errors specified for the routine 108.Xr write 2 , 109except that in case of 110.Fa stream 111being a read-only descriptor, 112.Fn fflush 113returns 0. 114.Sh SEE ALSO 115.Xr write 2 , 116.Xr fclose 3 , 117.Xr fopen 3 , 118.Xr setbuf 3 119.Sh STANDARDS 120The 121.Fn fflush 122function 123conforms to 124.St -isoC . 125.Sh HISTORY 126The 127.Fn fflush 128function first appeared in 129.At v4 . 130The 131.Fn fpurge 132function first appeared in 133.Bx 4.4 . 134