lseek64

LSEEK64(3)                 Linux Programmer's Manual                LSEEK64(3)

NAME
       lseek64 - reposition 64-bit read/write file offset

SYNOPSIS
       #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);

DESCRIPTION
       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 compi-
       lation.

       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.

ATTRIBUTES
       For an  explanation  of  the  terms  used  in  this  section,  see  at-
       tributes(7).

       +----------+---------------+---------+
       |Interface | Attribute     | Value   |
       +----------+---------------+---------+
       |lseek64() | Thread safety | MT-Safe |
       +----------+---------------+---------+
NOTES
       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 ap-
       plications 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  fea-
       ture  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.

SEE ALSO
       llseek(2), lseek(2)

COLOPHON
       This  page  is  part of release 5.10 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/.

Linux                             2020-11-01                        LSEEK64(3)