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.\" 34.Dd May 1, 2020 35.Dt FFLUSH 3 36.Os 37.Sh NAME 38.Nm fflush , 39.Nm fflush_unlocked , 40.Nm fpurge 41.Nd flush a stream 42.Sh LIBRARY 43.Lb libc 44.Sh SYNOPSIS 45.In stdio.h 46.Ft int 47.Fn fflush "FILE *stream" 48.Ft int 49.Fn fflush_unlocked "FILE *stream" 50.Ft int 51.Fn fpurge "FILE *stream" 52.Sh DESCRIPTION 53The function 54.Fn fflush 55forces a write of all buffered data for the given output or update 56.Fa stream 57via the stream's underlying write function. 58The open status of the stream is unaffected. 59.Pp 60If the 61.Fa stream 62argument is 63.Dv NULL , 64.Fn fflush 65flushes 66.Em all 67open output streams. 68.Pp 69The 70.Fn fflush_unlocked 71function is equivalent to 72.Fn fflush , 73except that the caller is responsible for locking the stream with 74.Xr flockfile 3 75before calling it. 76This function may be used to avoid the overhead of locking the stream and to 77prevent races when multiple threads are operating on the same stream. 78.Pp 79The function 80.Fn fpurge 81erases any input or output buffered in the given 82.Fa stream . 83For output streams this discards any unwritten output. 84For input streams this discards any input read from the underlying object 85but not yet obtained via 86.Xr getc 3 ; 87this includes any text pushed back via 88.Xr ungetc 3 . 89.Sh RETURN VALUES 90Upon successful completion 0 is returned. 91Otherwise, 92.Dv EOF 93is returned and the global variable 94.Va errno 95is set to indicate the error. 96.Sh ERRORS 97.Bl -tag -width Er 98.It Bq Er EBADF 99The 100.Fa stream 101argument 102is not an open stream. 103.El 104.Pp 105The function 106.Fn fflush 107may also fail and set 108.Va errno 109for any of the errors specified for the routine 110.Xr write 2 , 111except that in case of 112.Fa stream 113being a read-only descriptor, 114.Fn fflush 115returns 0. 116.Sh SEE ALSO 117.Xr write 2 , 118.Xr fclose 3 , 119.Xr fopen 3 , 120.Xr setbuf 3 121.Sh STANDARDS 122The 123.Fn fflush 124function 125conforms to 126.St -isoC . 127.Sh HISTORY 128The 129.Fn fflush 130function first appeared in 131.At v4 . 132The 133.Fn fpurge 134function first appeared in 135.Bx 4.4 . 136