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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(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).

   lseek()
   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.

   lseek64()
   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().

   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.

   _llseek()
   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.

ATTRIBUTES

   For   an   explanation   of   the  terms  used  in  this  section,  see
   attributes(7).

   
   Interface  Attribute      Value   
   
   lseek64()  Thread safety  MT-Safe

SEE ALSO

   llseek(2), lseek(2)

COLOPHON

   This page is part of release 4.09 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/.



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