This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface

       None.

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard
       for Information  Technology  --  Portable  Operating  System  Interface  (POSIX),  The  Open  Group  Base
       Specifications  Issue  7, 2018 Edition, Copyright (C) 2018 by the Institute of Electrical and Electronics
       Engineers, Inc and The Open Group.  In the event of any discrepancy between this version and the original
       IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee  document.
       The original Standard can be obtained online at http://www.opengroup.org/unix/online.html .

       Any  typographical  or formatting errors that appear in this page are most likely to have been introduced
       during  the  conversion  of  the  source  files  to  man  page  format.  To  report  such   errors,   see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group                                   2017                                         LSEEK(3POSIX)

       The  lseek()  function  shall  set the file offset for the open file description associated with the file
       descriptor fildes, as follows:

        *  If whence is SEEK_SET, the file offset shall be set to offset bytes.

        *  If whence is SEEK_CUR, the file offset shall be set to its current location plus offset.

        *  If whence is SEEK_END, the file offset shall be set to the size of the file plus offset.

       The symbolic constants SEEK_SET, SEEK_CUR, and SEEK_END are defined in <unistd.h>.

       The behavior of lseek() on devices which are incapable of seeking is implementation-defined.   The  value
       of the file offset associated with such a device is undefined.

       The  lseek()  function  shall  allow the file offset to be set beyond the end of the existing data in the
       file. If data is later written at this point, subsequent reads of data in the gap shall return bytes with
       the value 0 until data is actually written into the gap.

       The lseek() function shall not, by itself, extend the size of a file.

       If fildes refers to a shared memory object, the result of the lseek() function is unspecified.

       If fildes refers to a typed memory object, the result of the lseek() function is unspecified.

       The lseek() function shall fail if:

       EBADF  The fildes argument is not an open file descriptor.

       EINVAL The whence argument is not a proper value, or the resulting file offset would be  negative  for  a
              regular file, block special file, or directory.

       EOVERFLOW
              The  resulting  file offset would be a value which cannot be represented correctly in an object of
              type off_t.

       ESPIPE The fildes argument is associated with a pipe, FIFO, or socket.

       Thefollowingsectionsareinformative.

       None.

       None.

       lseek — move the read/write file offset

       This  manual  page  is part of the POSIX Programmer's Manual.  The Linux implementation of this interface
       may differ (consult the corresponding Linux manual page for details of Linux behavior), or the  interface
       may not be implemented on Linux.

       The ISO C standard includes the functions fgetpos() and fsetpos(), which work on very large files by  use
       of a special positioning type.

       Although  lseek()  may position the file offset beyond the end of the file, this function does not itself
       extend the size of the file. While the only function in POSIX.1‐2008 that may directly extend the size of
       the file is write(), truncate(), and ftruncate(), several functions originally  derived  from  the  ISO C
       standard, such as fwrite(), fprintf(), and so on, may do so (by causing calls on write()).

       An  invalid  file  offset that would cause [EINVAL] to be returned may be both implementation-defined and
       device-dependent (for example, memory may have few invalid values). A negative file offset may  be  valid
       for some devices in some implementations.

       The  POSIX.1‐1990  standard  did  not  specifically  prohibit  lseek()  from returning a negative offset.
       Therefore, an application was required to clear errno prior to the call and check errno  upon  return  to
       determine  whether  a  return  value  of  (off_t)-1  is  a  negative  offset or an indication of an error
       condition. The standard developers did not wish to require this  action  on  the  part  of  a  conforming
       application,  and  chose to require that errno be set to [EINVAL] when the resulting file offset would be
       negative for a regular file, block special file, or directory.

       Upon successful completion, the resulting offset, as measured in bytes from the beginning  of  the  file,
       shall  be  returned.  Otherwise,  -1 shall be returned, errno shall be set to indicate the error, and the
       file offset shall remain unchanged.

open()

       The Base Definitions volume of POSIX.1‐2017, <sys_types.h>, <unistd.h>

       #include <unistd.h>

       off_t lseek(int fildes, off_t offset, int whence);