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NAME | LIBRARY | SYNOPSIS | DESCRIPTION | ATTRIBUTES | NOTES | SEE ALSO | COLOPHON |
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lseek64(3) Library Functions Manual lseek64(3)
lseek64 - reposition 64-bit read/write file offset
Standard C library (libc, -lc)
#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().
lseek()
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.
lseek64()
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.
llseek()
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.
_llseek()
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.
llseek(2), lseek(2)
This page is part of the man-pages (Linux kernel and C library
user-space interface documentation) project. Information about
the project can be found at
⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report
for this manual page, see
⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
This page was obtained from the tarball man-pages-6.9.1.tar.gz
fetched from
⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on
2024-06-26. If you discover any rendering problems in this HTML
version of the page, or you believe there is a better or more up-
to-date source for the page, or you have corrections or
improvements to the information in this COLOPHON (which is not
part of the original manual page), send a mail to
man-pages@man7.org
Linux man-pages 6.9.1 2024-05-02 lseek64(3)
Pages that refer to this page: llseek(2), lseek(2), off_t(3type)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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