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(2) 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(2),
lseek64(),
llseek(2), and
_llseek(2).
Prototype:
off_t lseek(int fd, off_t offset, int whence);
lseek(2) 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 library routine
lseek64() 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, and is defined to be
an alias for
llseek().
Prototype:
loff_t llseek(int fd, loff_t offset, int whence);
The type
loff_t is a 64-bit signed type. The library routine
llseek() 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.
On 32-bit architectures, this is the system call that is used 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 |
llseek(2),
lseek(2)