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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.\" manual page may be incorrect or out-of-date.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 2013-08-19 "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>
.sp
.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.
.LP
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 the raw system call
.BR _llseek (2).
.SS lseek
Prototype:
.nf
.sp
.in +4n
.BI "off_t lseek(int " fd ", off_t " offset ", int " whence );
.in
.fi
.sp
.BR lseek (2)
uses the type
.IR off_t .
This is a 32-bit signed type on 32-bit architectures, unless one
compiles with
.nf
.sp
.in +4n
#define _FILE_OFFSET_BITS 64
.in
.sp
.fi
in which case it is a 64-bit signed type.
.SS lseek64
Prototype:
.nf
.sp
.in +4n
.BI "off64_t lseek64(int " fd ", off64_t " offset ", int " whence );
.in
.fi
.sp
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
.nf
.sp
.in +4n
#define _LARGEFILE64_SOURCE
.in
.sp
.fi
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:
.nf
.sp
.in +4n
.BI "loff_t llseek(int " fd ", loff_t " offset ", int " whence );
.in
.fi
.sp
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 libc5 and glibc and works without special defines.
Its prototype was given in
.I <unistd.h>
with libc5, but glibc does not provide a prototype.
This is bad, since a prototype is needed.
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
.sp
.in +4n
"the \`llseek\' function may be dangerous; use \`lseek64\' instead."
.in
.sp
This makes this function unusable if one desires a warning-free
compilation.
.SS _llseek
All the above functions are implemented in terms of this system call.
The prototype is:
.nf
.sp
.in +4n
.BI "int _llseek(int " fd ", off_t " offset_hi ", off_t " offset_lo ,
.BI " loff_t *" result ", int " whence );
.in
.fi
.sp
For more details, see
.BR llseek (2).
.SH ATTRIBUTES
.SS Multithreading (see pthreads(7))
The
.BR lseek64 ()
function is thread-safe.
.SH SEE ALSO
.BR llseek (2),
.BR lseek (2)
|
