lseek64(3) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | ATTRIBUTES | NOTES | SEE ALSO | COLOPHON

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

NAME         top

       lseek64 - reposition 64-bit read/write file offset

SYNOPSIS         top

       #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         top

       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
       compilation.

       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         top

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

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

NOTES         top

       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 applications 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 feature 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         top

       llseek(2), lseek(2)

COLOPHON         top

       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)

Pages that refer to this page: llseek(2)lseek(2)