FXGSEEK Name
FXGSEEK
Author
Craig B. Markwardt, NASA/GSFC Code 662, Greenbelt, MD 20770
craigm@lheamail.gsfc.nasa.gov
UPDATED VERSIONs can be found on my WEB PAGE:
http://cow.physics.wisc.edu/~craigm/idl/idl.html
Purpose
Perform a seek operation on a generic resource.
Major Topics
File I/O, Pipes, URLs, FITS Calling Sequence
FXGSEEK, UNIT, POSITION ;; Sets the current file position
FXGSEEK, -UNIT, POSITION ;; Queries the current file position
Description
FXGSEEK performs a seek on the selected resource. Depending on
the sign of UNIT, the current file position is either queried or
set, in much the same manner as the built-in IDL procedure
POINT_LUN.
If the resource is a stream, the seek operation does not
necessarily force a read until FXGREAD is called (i.e., reads are
"lazy").
You must use the specialized 'FXG' style functions to read, write
and seek on file units opened with FXGOPEN:
FXGOPEN - open resource
FXGCLOSE - close resource
FXGREAD - read from resource
FXGWRITE - write to resource
FXGSEEK - seek on resource (i.e., perform POINT_LUN)
FXGFILTERED - determine if resource is a normal file.
Inputs
UNIT - the unit number to operate on. The unit must have been
previously opened by FXGOPEN. The operation of FXGSEEK
depends on the sign of UNIT. If UNIT is positive, then the
current file position of file UNIT is set to POSITION. If
UNIT is negative, then the current file position of file
|UNIT| is placed in the variable POSITION.
POSITION - Depending on the sign of UNIT, the behavior is
different. When UNIT is positive, POSITION is an input
variable containing the new file position. When UNIT
is negative, POSITION is an output variable to contain
the file's current file position.
Modification History
Written, 1999, CM
Documented, 02 Oct 1999, CM
Changed copyright notice, 21 Sep 2000, CM