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(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 5.08 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                              2017-09-15                         LSEEK64(3)