1.\" Copyright (c) 1980, 1991, 1993 2.\" The Regents of the University of California. All rights reserved. 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 1. Redistributions of source code must retain the above copyright 8.\" notice, this list of conditions and the following disclaimer. 9.\" 2. Redistributions in binary form must reproduce the above copyright 10.\" notice, this list of conditions and the following disclaimer in the 11.\" documentation and/or other materials provided with the distribution. 12.\" 3. All advertising materials mentioning features or use of this software 13.\" must display the following acknowledgement: 14.\" This product includes software developed by the University of 15.\" California, Berkeley and its contributors. 16.\" 4. 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.\" @(#)lseek.2 8.3 (Berkeley) 4/19/94 33.\" $FreeBSD: src/lib/libc/sys/lseek.2,v 1.10.2.6 2001/12/14 18:34:01 ru Exp $ 34.\" $DragonFly: src/lib/libc/sys/lseek.2,v 1.2 2003/06/17 04:26:47 dillon Exp $ 35.\" 36.Dd April 19, 1994 37.Dt LSEEK 2 38.Os 39.Sh NAME 40.Nm lseek 41.Nd reposition read/write file offset 42.Sh LIBRARY 43.Lb libc 44.Sh SYNOPSIS 45.In unistd.h 46.Ft off_t 47.Fn lseek "int fildes" "off_t offset" "int whence" 48.Sh DESCRIPTION 49The 50.Fn lseek 51function repositions the offset of the file descriptor 52.Fa fildes 53to the 54argument 55.Fa offset 56according to the directive 57.Fa whence . 58The argument 59.Fa fildes 60must be an open 61file descriptor. 62.Fn Lseek 63repositions the file position pointer associated with the file 64descriptor 65.Fa fildes 66as follows: 67.Bl -item -offset indent 68.It 69If 70.Fa whence 71is 72.Dv SEEK_SET , 73the offset is set to 74.Fa offset 75bytes. 76.It 77If 78.Fa whence 79is 80.Dv SEEK_CUR , 81the offset is set to its current location plus 82.Fa offset 83bytes. 84.It 85If 86.Fa whence 87is 88.Dv SEEK_END , 89the offset is set to the size of the 90file plus 91.Fa offset 92bytes. 93.El 94.Pp 95The 96.Fn lseek 97function allows the file offset to be set beyond the end 98of the existing end-of-file of the file. 99If data is later written 100at this point, subsequent reads of the data in the gap return 101bytes of zeros (until data is actually written into the gap). 102.Pp 103Some devices are incapable of seeking. The value of the pointer 104associated with such a device is undefined. 105.Sh RETURN VALUES 106Upon successful completion, 107.Fn lseek 108returns the resulting offset location as measured in bytes from the 109beginning of the file. 110Otherwise, 111a value of -1 is returned and 112.Va errno 113is set to indicate 114the error. 115.Sh ERRORS 116.Fn Lseek 117will fail and the file position pointer will remain unchanged if: 118.Bl -tag -width Er 119.It Bq Er EBADF 120.Em Fildes 121is not an open file descriptor. 122.It Bq Er ESPIPE 123.Em Fildes 124is associated with a pipe, socket, or FIFO. 125.It Bq Er EINVAL 126.Fa Whence 127is not a proper value. 128.El 129.Sh SEE ALSO 130.Xr dup 2 , 131.Xr open 2 132.Sh BUGS 133This document's use of 134.Fa whence 135is incorrect English, but is maintained for historical reasons. 136.Sh STANDARDS 137The 138.Fn lseek 139function call is expected to conform to 140.St -p1003.1-90 . 141.Sh HISTORY 142A 143.Fn lseek 144function call appeared in 145.At v7 . 146