LISP文件存在查询的求助！

littlebugk · 发表于 2004-6-1 10:39:00

请问要在lisp程序中要加入一个块，怎么判定该块名是否存在，比如要先建立一个块，插入各点：
(command "color" "1")
(setq t21c (polar t21 0 30));插入点t21c---------------------------
(setq ccd1 "1.6")

(setq ch 3.5)
(setq ch1 (* ch 1.61658))
(setq cp1 (polar t21c (/ pi 3) (* 2 ch1)))
(setq cp2 (polar t21c (/ pi 3) ch1))
(setq cp3 (polar cp2 pi ch1))
(setq cp4 (polar t21c (/ pi 2) (* 1.4 ch1)))
(command "pline" cp2 cp3 t21c cp1 "")
(setq cc1 (entlast))
(command "text" "m" cp4 ch "0" ccd1)
(setq cc2 (entlast))
;(command "-block" "c63" t21c cc1 cc2    "");块c63-------------------
(setq t7c (polar t7 (/ pi 2) 5));粗糙度标注点1(270度);-------------
(setq t0c (polar t0 (* pi 1.5) r));粗糙度标注点2(0度)--------------
(setq p5c (polar p5 (* pi 1.5) 20 ));粗糙度标注点3(270度)----------
(command "insert" "c63" "r" "0" t21c "" "" "")
(command "insert" "c63" "r" "270" t7c "" "" "")
(command "insert" "c63" "r" "0" t0c "" "" "")
(command "insert" "c63" "r" "270" p5c "" "" "")
但是第二次以后运行就会出现重定义，如何实现判定该块不存在的时候才定义成块！