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 April 2, 2022 33.Dt FERROR 3 34.Os 35.Sh NAME 36.Nm clearerr , 37.Nm clearerr_unlocked , 38.Nm feof , 39.Nm feof_unlocked , 40.Nm ferror , 41.Nm ferror_unlocked , 42.Nm fileno , 43.Nm fileno_unlocked 44.Nd check and reset stream status 45.Sh LIBRARY 46.Lb libc 47.Sh SYNOPSIS 48.In stdio.h 49.Ft void 50.Fn clearerr "FILE *stream" 51.Ft void 52.Fn clearerr_unlocked "FILE *stream" 53.Ft int 54.Fn feof "FILE *stream" 55.Ft int 56.Fn feof_unlocked "FILE *stream" 57.Ft int 58.Fn ferror "FILE *stream" 59.Ft int 60.Fn ferror_unlocked "FILE *stream" 61.Ft int 62.Fn fileno "FILE *stream" 63.Ft int 64.Fn fileno_unlocked "FILE *stream" 65.Sh DESCRIPTION 66The function 67.Fn clearerr 68clears the end-of-file and error indicators for the stream pointed 69to by 70.Fa stream . 71.Pp 72The function 73.Fn feof 74tests the end-of-file indicator for the stream pointed to by 75.Fa stream , 76returning non-zero if it is set. 77The end-of-file indicator may be cleared by explicitly calling 78.Fn clearerr , 79or as a side-effect of other operations, e.g.\& 80.Fn fseek . 81.Pp 82The function 83.Fn ferror 84tests the error indicator for the stream pointed to by 85.Fa stream , 86returning non-zero if it is set. 87.Pp 88The function 89.Fn fileno 90examines the argument 91.Fa stream 92and returns its integer descriptor. 93.Pp 94The 95.Fn clearerr_unlocked , 96.Fn feof_unlocked , 97.Fn ferror_unlocked , 98and 99.Fn fileno_unlocked 100functions are equivalent to 101.Fn clearerr , 102.Fn feof , 103.Fn ferror , 104and 105.Fn fileno 106respectively, except that the caller is responsible for locking the stream 107with 108.Xr flockfile 3 109before calling them. 110These functions may be used to avoid the overhead of locking the stream 111and to prevent races when multiple threads are operating on the same stream. 112.Sh ERRORS 113These functions should not fail and do not set the external 114variable 115.Va errno . 116.Sh SEE ALSO 117.Xr open 2 , 118.Xr fdopen 3 , 119.Xr flockfile 3 , 120.Xr stdio 3 121.Sh STANDARDS 122The functions 123.Fn clearerr , 124.Fn feof , 125and 126.Fn ferror 127conform to 128.St -isoC . 129.Sh HISTORY 130The functions 131.Fn clearerr , 132.Fn feof , 133.Fn ferror , 134and 135.Fn fileno 136first appeared in 137.At v7 . 138