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.\" Copyright 2004 Andries Brouwer <aeb@cwi.nl>.
.\"
.\" %%%LICENSE_START(VERBATIM)
.\" Permission is granted to make and distribute verbatim copies of this
.\" manual provided the copyright notice and this permission notice are
.\" preserved on all copies.
.\"
.\" Permission is granted to copy and distribute modified versions of this
.\" manual under the conditions for verbatim copying, provided that the
.\" entire resulting derived work is distributed under the terms of a
.\" permission notice identical to this one.
.\"
.\" Since the Linux kernel and libraries are constantly changing, this
.\" manual page may be incorrect or out-of-date. The author(s) assume no
.\" responsibility for errors or omissions, or for damages resulting from
.\" the use of the information contained herein. The author(s) may not
.\" have taken the same level of care in the production of this manual,
.\" which is licensed free of charge, as they might when working
.\" professionally.
.\"
.\" Formatted or processed versions of this manual, if unaccompanied by
.\" the source, must acknowledge the copyright and authors of this work.
.\" %%%LICENSE_END
.\"
.TH LSEEK64 3 2020-11-01 "Linux" "Linux Programmer's Manual"
.SH NAME
lseek64 \- reposition 64-bit read/write file offset
.SH SYNOPSIS
.BR "#define _LARGEFILE64_SOURCE" " /* See feature_test_macros(7) */"
.br
.B #include <sys/types.h>
.br
.B #include <unistd.h>
.PP
.BI "off64_t lseek64(int " fd ", off64_t " offset ", int " whence );
.SH DESCRIPTION
The
.BR lseek (2)
family of functions reposition the offset of the open file associated
with the file descriptor
.I fd
to
.I offset
bytes relative to the start, current position, or end of the file,
when
.I whence
has the value
.BR SEEK_SET ,
.BR SEEK_CUR ,
or
.BR SEEK_END ,
respectively.
.PP
For more details, return value, and errors, see
.BR lseek (2).
.PP
Four interfaces are available:
.BR lseek (2),
.BR lseek64 (),
.BR llseek (2),
and
.BR _llseek (2).
.SS lseek()
Prototype:
.PP
.in +4n
.EX
.BI "off_t lseek(int " fd ", off_t " offset ", int " whence );
.EE
.in
.PP
.BR lseek (2)
uses the type
.IR off_t .
This is a 32-bit signed type on 32-bit architectures, unless one
compiles with
.PP
.in +4n
.EX
#define _FILE_OFFSET_BITS 64
.EE
.in
.PP
in which case it is a 64-bit signed type.
.SS lseek64()
Prototype:
.PP
.in +4n
.EX
.BI "off64_t lseek64(int " fd ", off64_t " offset ", int " whence );
.EE
.in
.PP
The library routine
.BR lseek64 ()
uses a 64-bit type even when
.I off_t
is a 32-bit type.
Its prototype (and the type
.IR off64_t )
is available only when one compiles with
.PP
.in +4n
.EX
#define _LARGEFILE64_SOURCE
.EE
.in
.PP
The function
.BR lseek64 ()
.\" in glibc 2.0.94, not in 2.0.6
is available since glibc 2.1, and is defined to be an alias for
.BR llseek ().
.SS llseek()
Prototype:
.PP
.in +4n
.EX
.BI "loff_t llseek(int " fd ", loff_t " offset ", int " whence );
.EE
.in
.PP
The type
.I loff_t
is a 64-bit signed type.
The library routine
.BR llseek ()
.\" in libc 5.0.9, not in 4.7.6
is available in glibc and works without special defines.
However, the glibc headers do not provide a prototype.
Users should add
the above prototype, or something equivalent, to their own source.
When users complained about data loss caused by a miscompilation of
.BR e2fsck (8),
glibc 2.1.3 added the link-time warning
.PP
.in +4n
"the \`llseek\' function may be dangerous; use \`lseek64\' instead."
.in
.PP
This makes this function unusable if one desires a warning-free
compilation.
Since glibc 2.28,
.\" glibc commit 5c5c0dd747070db624c8e2c43691cec854f114ef
this function symbol is no longer available to newly linked applications.
.\"
.SS _llseek()
On 32-bit architectures,
this is the system call that is used to implement all of the above functions.
The prototype is:
.PP
.in +4n
.EX
.BI "int _llseek(int " fd ", off_t " offset_hi ", off_t " offset_lo ,
.BI " loff_t *" result ", int " whence );
.EE
.in
.PP
For more details, see
.BR llseek (2).
.PP
64-bit systems don't need an
.BR _llseek ()
system call.
Instead, they have an
.BR lseek (2)
system call that supports 64-bit file offsets.
.SH ATTRIBUTES
For an explanation of the terms used in this section, see
.BR attributes (7).
.TS
allbox;
lb lb lb
l l l.
Interface Attribute Value
T{
.BR lseek64 ()
T} Thread safety MT-Safe
.TE
.SH SEE ALSO
.BR llseek (2),
.BR lseek (2)
.SH COLOPHON
This page is part of release 5.09 of the Linux
.I man-pages
project.
A description of the project,
information about reporting bugs,
and the latest version of this page,
can be found at
\%https://www.kernel.org/doc/man\-pages/.
|
