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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).

       ┌──────────┬───────────────┬─────────┐
       │InterfaceAttributeValue   │
       ├──────────┼───────────────┼─────────┤
       │lseek64() │ Thread safety │ MT-Safe │
       └──────────┴───────────────┴─────────┘

SEE ALSO

       llseek(2), lseek(2)

COLOPHON

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