lseek64 — reposition 64-bit read/write file offset
#define _LARGEFILE64_SOURCE /* See feature_test_macros(7) */ #include <sys/types.h> #include <unistd.h>
off64_t
lseek64( |
int fd, |
| off64_t offset, | |
int whence); |
The lseek() family of
functions reposition the offset of the open file associated
with the file descriptor fd to offset bytes relative to the
start, current position, or end of the file, when whence has the value
SEEK_SET, SEEK_CUR, or SEEK_END, respectively.
For more details, return value, and errors, see lseek(2).
Four interfaces are available: lseek(), lseek64(), llseek(), and _llseek().
Prototype:
off_t lseek(int fd,off_t offset,int whence);
The C library's lseek()
wrapper function uses the type off_t. This is a 32-bit signed type on 32-bit
architectures, unless one compiles with
#define _FILE_OFFSET_BITS 64
in which case it is a 64-bit signed type.
Prototype:
off64_t lseek64(int fd,off64_t offset,int whence);
The lseek64() library
function uses a 64-bit type even when off_t is a 32-bit type. Its prototype (and
the type off64_t) is available
only when one compiles with
#define _LARGEFILE64_SOURCE
The function lseek64() is
available since glibc 2.1.
Prototype:
loff_t llseek(int fd,loff_t offset,int whence);
The type loff_t is a 64-bit
signed type. The llseek()
library function 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
e2fsck(8), glibc 2.1.3 added
the link-time warning
"the “llseek” function may be dangerous; use “lseek64” instead."
This makes this function unusable if one desires a warning-free compilation.
Since glibc 2.28, this function symbol is no longer available to newly linked applications.
On 32-bit architectures, this is the system call that is used (by the C library wrapper functions) to implement all of the above functions. The prototype is:
int _llseek(int fd,off_t offset_hi,off_t offset_lo,loff_t *result,int whence);
For more details, see llseek(2).
64-bit systems don't need an _llseek() system call. Instead, they have
an lseek(2) system call that
supports 64-bit file offsets.
For an explanation of the terms used in this section, see attributes(7).
| Interface | Attribute | Value |
lseek64() |
Thread safety | MT-Safe |
lseek64() is one of the
functions that was specified in the Large File Summit (LFS)
specification that was completed in 1996. The purpose of the
specification was to provide transitional support that
allowed applications on 32-bit systems to access files whose
size exceeds that which can be represented with a 32-bit
off_t type. As noted above, this
symbol is exposed by header files if the _LARGEFILE64_SOURCE feature test macro is
defined. ALternatively, on a 32-bit system, the symbol
lseek is aliased to
lseek64 if the macro
_FILE_OFFSET_BITS is defined
with the value 64.
This page is part of release 5.11 of the Linux 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/.
|
Copyright 2004 Andries Brouwer <aebcwi.nl>. and Copyright (c) 2020 Michael Kerrisk <mtk.manpagesgmail.com> %%%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 |