4.3BSD - /usr/man/cat2/lseek.0

LSEEK(2)                                                              LSEEK(2)


NAME
       lseek - move read/write pointer

SYNOPSIS
       #include <sys/file.h>

       #define L_SET   0 /* set the seek pointer */
       #define L_INCR  1 /* increment the seek pointer */
       #define L_XTND  2 /* extend the file size */

       pos = lseek(d, offset, whence)
       off_t pos;
       int d;
       off_t offset;
       int whence;

DESCRIPTION
       The  descriptor  d  refers  to a file or device open for reading and/or
       writing.  Lseek sets the file pointer of d as follows:

              If whence is L_SET, the pointer is set to offset bytes.

              If whence is L_INCR, the pointer is set to its current  location
              plus offset.

              If  whence is L_XTND, the pointer is set to the size of the file
              plus offset.

       Upon successful completion, the resulting pointer location as  measured
       in  bytes  from  beginning  of  the file is returned.  Some devices are
       incapable of seeking.  The value of the pointer associated with such  a
       device is undefined.

NOTES
       Seeking  far  beyond  the end of a file, then writing, creates a gap or
       “hole”, which occupies no physical space and reads as zeros.

RETURN VALUE
       Upon successful completion, the current file pointer value is returned.
       Otherwise,  a  value of -1 is returned and errno is set to indicate the
       error.

ERRORS
       Lseek will fail and the file pointer will remain unchanged if:

       [EBADF]        Fildes is not an open file descriptor.

       [ESPIPE]       Fildes is associated with a pipe or a socket.

       [EINVAL]       Whence is not a proper value.

SEE ALSO
       dup(2), open(2)

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


4th Berkeley Distribution      February 24, 1986                      LSEEK(2)