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LSEEK(2)                   Linux Programmer's Manual                  LSEEK(2)



NAME
       lseek - reposition read/write file offset

SYNOPSIS
       #include <sys/types.h>
       #include <unistd.h>

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

DESCRIPTION
       The  lseek()  function  repositions the offset of the open file associated with the
       file descriptor fd to the argument offset according to the directive whence as fol-
       lows:

       SEEK_SET
              The offset is set to offset bytes.

       SEEK_CUR
              The offset is set to its current location plus offset bytes.

       SEEK_END
              The offset is set to the size of the file plus offset bytes.

       The  lseek()  function  allows the file offset to be set beyond the end of the file
       (but this does not change the size of the file).  If data is later written at  this
       point,  subsequent reads of the data in the gap (a "hole") return null bytes ('\0')
       until data is actually written into the gap.

RETURN VALUE
       Upon successful completion, lseek() returns the resulting offset location  as  mea-
       sured in bytes from the beginning of the file.  Otherwise, a value of (off_t) -1 is
       returned and errno is set to indicate the error.

ERRORS
       EBADF  fd is not an open file descriptor.

       EINVAL whence is not one of SEEK_SET, SEEK_CUR, SEEK_END;  or  the  resulting  file
              offset would be negative, or beyond the end of a seekable device.

       EOVERFLOW
              The resulting file offset cannot be represented in an off_t.

       ESPIPE fd is associated with a pipe, socket, or FIFO.

CONFORMING TO
       SVr4, 4.3BSD, POSIX.1-2001.

NOTES
       This  document's  use of whence is incorrect English, but maintained for historical
       reasons.

       Some devices are incapable of seeking and POSIX does not specify which devices must
       support lseek().

       On Linux, using lseek() on a tty device returns ESPIPE.

       When converting old code, substitute values for whence with the following macros:

        old       new
       0        SEEK_SET
       1        SEEK_CUR

       2        SEEK_END
       L_SET    SEEK_SET
       L_INCR   SEEK_CUR
       L_XTND   SEEK_END

       SVr1-3 returns long instead of off_t, BSD returns int.

       Note  that  file  descriptors  created  by dup(2) or fork(2) share the current file
       position pointer, so seeking on such files may be subject to race conditions.

SEE ALSO
       dup(2), fork(2), open(2), fseek(3), lseek64(3), posix_fallocate(3)

COLOPHON
       This page is part of release 3.22 of the Linux man-pages project.  A description of
       the  project, and information about reporting bugs, can be found at http://www.ker-
       nel.org/doc/man-pages/.



Linux                             2001-09-24                          LSEEK(2)

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