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.\" 35.Dd April 19, 1994 36.Dt LSEEK 2 37.Os 38.Sh NAME 39.Nm lseek 40.Nd reposition read/write file offset 41.Sh LIBRARY 42.Lb libc 43.Sh SYNOPSIS 44.In unistd.h 45.Ft off_t 46.Fn lseek "int fildes" "off_t offset" "int whence" 47.Sh DESCRIPTION 48The 49.Fn lseek 50function repositions the offset of the file descriptor 51.Fa fildes 52to the 53argument 54.Fa offset 55according to the directive 56.Fa whence . 57The argument 58.Fa fildes 59must be an open 60file descriptor. 61.Fn Lseek 62repositions the file position pointer associated with the file 63descriptor 64.Fa fildes 65as follows: 66.Bl -item -offset indent 67.It 68If 69.Fa whence 70is 71.Dv SEEK_SET , 72the offset is set to 73.Fa offset 74bytes. 75.It 76If 77.Fa whence 78is 79.Dv SEEK_CUR , 80the offset is set to its current location plus 81.Fa offset 82bytes. 83.It 84If 85.Fa whence 86is 87.Dv SEEK_END , 88the offset is set to the size of the 89file plus 90.Fa offset 91bytes. 92.El 93.Pp 94The 95.Fn lseek 96function allows the file offset to be set beyond the end 97of the existing end-of-file of the file. 98If data is later written 99at this point, subsequent reads of the data in the gap return 100bytes of zeros (until data is actually written into the gap). 101.Pp 102Some devices are incapable of seeking. The value of the pointer 103associated with such a device is undefined. 104.Sh RETURN VALUES 105Upon successful completion, 106.Fn lseek 107returns the resulting offset location as measured in bytes from the 108beginning of the file. 109Otherwise, 110a value of -1 is returned and 111.Va errno 112is set to indicate 113the error. 114.Sh ERRORS 115.Fn Lseek 116will fail and the file position pointer will remain unchanged if: 117.Bl -tag -width Er 118.It Bq Er EBADF 119.Em Fildes 120is not an open file descriptor. 121.It Bq Er ESPIPE 122.Em Fildes 123is associated with a pipe, socket, or FIFO. 124.It Bq Er EINVAL 125.Fa Whence 126is not a proper value. 127.El 128.Sh SEE ALSO 129.Xr dup 2 , 130.Xr open 2 131.Sh BUGS 132This document's use of 133.Fa whence 134is incorrect English, but is maintained for historical reasons. 135.Sh STANDARDS 136The 137.Fn lseek 138function call is expected to conform to 139.St -p1003.1-90 . 140.Sh HISTORY 141A 142.Fn lseek 143function call appeared in 144.At v7 . 145