lseek64(3)

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(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  compi-
       lation.

   _llseek()
       On 32-bit architectures, this is the system call that is used to imple-
       ment 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 |
       +----------+---------------+---------+
SEE ALSO
       llseek(2), lseek(2)

COLOPHON
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       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                             2017-09-15                        LSEEK64(3)