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@(#)lseek.2 8.3 (Berkeley) 4/19/94
$FreeBSD: head/lib/libc/sys/lseek.2 59460 2000-04-21 09:42:15Z phantom $
.Dd April 19, 1994 .Dt LSEEK 2 .Os BSD 4 .Sh NAME .Nm lseek .Nd reposition read/write file offset .Sh LIBRARY .Lb libc .Sh SYNOPSIS .Fd #include <unistd.h> .Ft off_t .Fn lseek "int fildes" "off_t offset" "int whence" .Sh DESCRIPTION The .Fn lseek function repositions the offset of the file descriptor .Fa fildes to the argument .Fa offset according to the directive .Fa whence. The argument .Fa fildes must be an open file descriptor. .Fn Lseek repositions the file position pointer associated with the file descriptor .Fa fildes as follows: l -item -offset indent t If .Fa whence is .Dv SEEK_SET , the offset is set to .Fa offset bytes. t If .Fa whence is .Dv SEEK_CUR , the offset is set to its current location plus .Fa offset bytes. t If .Fa whence is .Dv SEEK_END , the offset is set to the size of the file plus .Fa offset bytes. .El
p The .Fn lseek function allows the file offset to be set beyond the end of the existing end-of-file of the file. If data is later written at this point, subsequent reads of the data in the gap return bytes of zeros (until data is actually written into the gap).
p Some devices are incapable of seeking. The value of the pointer associated with such a device is undefined. .Sh RETURN VALUES Upon successful completion, .Fn lseek returns the resulting offset location as measured in bytes from the beginning of the file. Otherwise, a value of -1 is returned and .Va errno is set to indicate the error. .Sh ERRORS .Fn Lseek will fail and the file position pointer will remain unchanged if: l -tag -width [EINVAL] t Bq Er EBADF .Em Fildes is not an open file descriptor. t Bq Er ESPIPE .Em Fildes is associated with a pipe, socket, or FIFO. t Bq Er EINVAL .Fa Whence is not a proper value. .El .Sh SEE ALSO .Xr dup 2 , .Xr open 2 .Sh BUGS This document's use of .Fa whence is incorrect English, but is maintained for historical reasons. .Sh STANDARDS The .Fn lseek function call is expected to conform to .St -p1003.1-90 . .Sh HISTORY A .Fn lseek function call appeared in .At v7 .