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NAME

       lseek - reposition read/write file offset

SYNOPSIS

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

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

DESCRIPTION

       The lseek() function repositions the offset of the open file associated
       with the file descriptor fildes to the argument offset according to the
       directive whence as follows:

       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 existing end-of-file 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 return bytes of zeros (until  data  is  actually
       written into the gap).

RETURN VALUE

       Upon  successful  completion,  lseek()  returns  the  resulting  offset
       location  as  measured  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  fildes 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.

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

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

CONFORMING TO

       SVr4, POSIX, 4.3BSD

RESTRICTIONS

       Some  devices are incapable of seeking and POSIX does not specify which
       devices must support it.

       Linux specific restrictions: using lseek()  on  a  tty  device  returns
       ESPIPE.

NOTES

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

       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)