4.3BSD-UWisc/man/cat2/lseek.2

LSEEK(2)            UNIX Programmer's Manual             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.  _L_s_e_e_k sets the file pointer of _d as fol-
     lows:

          If _w_h_e_n_c_e is L_SET, the pointer is set to _o_f_f_s_e_t bytes.

          If _w_h_e_n_c_e is L_INCR, the pointer is set to its current
          location plus _o_f_f_s_e_t.

          If _w_h_e_n_c_e is L_XTND, the pointer is set to the size of
          the file plus _o_f_f_s_e_t.

     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 _e_r_r_n_o
     is set to indicate the error.

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

     [EBADF]        _F_i_l_d_e_s is not an open file descriptor.

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




Printed 12/27/86        February 24, 1986                       1






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



     [EINVAL]       _W_h_e_n_c_e is not a proper value.

SEE ALSO
     dup(2), open(2)

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















































Printed 12/27/86        February 24, 1986                       2