请教，以下内容要如何理解？

liuhaixin88

To set and restore system variables, you can also the ai_sysvar function.
This function is available in AutoCAD since a while.
It's defined in acaddoc20XX.lsp (ai_utils.lsp or acad.mnl in older versions), so it's automatically loaded in each document.

Quote

;;; --- ai_sysvar ------------------------------------------
;;; Change system variable settings and save current settings
;;; (Note: used by *merr* to restore system settings on error.)
;;;
;;; The <vars> argument is used to...
;;;   restore previous settings (ai_sysvar NIL)
;;;   set a single sys'var (ai_sysvar  '("cmdecho" . 0))
;;;   set multiple sys'vars (ai_sysvar '(("cmdecho" . 0)("gridmode" . 0)))
;;;
;;; defun-q is needed by Visual Lisp for functions which redefine themselves.
;;; it is aliased to defun for seamless use with AutoLISP.

Anywhere in the code, you can call ai_sysvar to save the current value of one or more sysvar and set it a new value (or not).

Example:

• 

  1. ;; save and set "osmode" to 0
     
  2. (ai_sysvar '("osmode" . 0))
     
  3. ...
     
  4. ;; save and set "orthomode" to 1 and only save "autosnap"
     
  5. (ai_sysvar '(("orthomode" . 1) ("autosnap" . nil)))
     
  6. ...
     
  7. ;; restor all sysvars
     
  8. (ai_sysvar nil)

  ;; save and set "osmode" to 0<br /> (ai_sysvar '("osmode" . 0))<br /> ...<br /> ;; save and set "orthomode" to 1 and only save "autosnap"<br /> (ai_sysvar '(("orthomode" . 1) ("autosnap" . nil)))<br /> ...<br /> ;; restor all sysvars<br /> (ai_sysvar nil)
  
  

<EDIT> I forgot to say, the implementation of ai_sysvar is quite interesting with the use of defun-q which allows to store the list of var names ans values within the function.

自贡黄明儒

找到ai_sysvar的定义，一切都清楚了
http://www.askcad.com/bbs/thread-47222-1-1.html