1.\" $NetBSD: lseek.2,v 1.8 1997/06/21 07:02:40 lukem Exp $ 2.\" 3.\" Copyright (c) 1980, 1991, 1993 4.\" The Regents of the University of California. All rights reserved. 5.\" 6.\" Redistribution and use in source and binary forms, with or without 7.\" modification, are permitted provided that the following conditions 8.\" are met: 9.\" 1. Redistributions of source code must retain the above copyright 10.\" notice, this list of conditions and the following disclaimer. 11.\" 2. Redistributions in binary form must reproduce the above copyright 12.\" notice, this list of conditions and the following disclaimer in the 13.\" documentation and/or other materials provided with the distribution. 14.\" 3. All advertising materials mentioning features or use of this software 15.\" must display the following acknowledgement: 16.\" This product includes software developed by the University of 17.\" California, Berkeley and its contributors. 18.\" 4. Neither the name of the University nor the names of its contributors 19.\" may be used to endorse or promote products derived from this software 20.\" without specific prior written permission. 21.\" 22.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 23.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 24.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 25.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 26.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 27.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 28.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 29.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 30.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 31.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 32.\" SUCH DAMAGE. 33.\" 34.\" @(#)lseek.2 8.3 (Berkeley) 4/19/94 35.\" 36.Dd April 19, 1994 37.Dt LSEEK 2 38.Os BSD 4 39.Sh NAME 40.Nm lseek 41.Nd reposition read/write file offset 42.Sh SYNOPSIS 43.Fd #include <unistd.h> 44.Ft off_t 45.Fn lseek "int fildes" "off_t offset" "int whence" 46.Sh DESCRIPTION 47The 48.Fn lseek 49function repositions the offset of the file descriptor 50.Fa fildes 51to the 52argument 53.Fa offset 54according to the directive 55.Fa whence . 56The argument 57.Fa fildes 58must be an open 59file descriptor. 60.Fn lseek 61repositions the file pointer 62.Fa fildes 63as follows: 64.Bl -item -offset indent 65.It 66If 67.Fa whence 68is 69.Dv SEEK_SET , 70the offset is set to 71.Fa offset 72bytes. 73.It 74If 75.Fa whence 76is 77.Dv SEEK_CUR , 78the offset is set to its current location plus 79.Fa offset 80bytes. 81.It 82If 83.Fa whence 84is 85.Dv SEEK_END , 86the offset is set to the size of the 87file plus 88.Fa offset 89bytes. 90.El 91.Pp 92The 93.Fn lseek 94function allows the file offset to be set beyond the end 95of the existing end-of-file of the file. If data is later written 96at this point, subsequent reads of the data in the gap return 97bytes of zeros (until data is actually written into the gap). 98.Pp 99Some devices are incapable of seeking. The value of the pointer 100associated with such a device is undefined. 101.Sh RETURN VALUES 102Upon successful completion, 103.Fn lseek 104returns the resulting offset location as measured in bytes from the 105beginning of the file. 106Otherwise, 107a value of -1 is returned and 108.Va errno 109is set to indicate 110the error. 111.Sh ERRORS 112.Fn Lseek 113will fail and the file pointer will remain unchanged if: 114.Bl -tag -width Er 115.It Bq Er EBADF 116.Em Fildes 117is not an open file descriptor. 118.It Bq Er ESPIPE 119.Em Fildes 120is associated with a pipe, socket, or FIFO. 121.It Bq Er EINVAL 122.Fa Whence 123is not a proper value, or the resulting file offset would be invalid. 124.El 125.Sh SEE ALSO 126.Xr dup 2 , 127.Xr open 2 128.Sh BUGS 129This document's use of 130.Fa whence 131is incorrect English, but is maintained for historical reasons. 132.Sh STANDARDS 133The 134.Fn lseek 135function conforms to 136.St -p1003.1-88 . 137