AutoLISP Tips'n'Tricks

Random number generation function - based on the linear congruential method as presented in Doug Cooper's book Condensed Pascal, pp. 116-117.

Returns a random number between 0 and 1 :

(defun randnum (/ modulus multiplier increment random)
  (if (not seed)
    (setq seed (getvar "DATE"))
  )
  (setq modulus    65536
        multiplier 25173
        increment  13849
        seed  (rem (+ (* multiplier seed) increment) modulus)
        random     (/ seed modulus)
  )
)

The following will give you a list of all entries in a symbol table. This is great for creating a list to populate a list box in DCL.

;;;Start Coding Here
 
(defun tablelist (s / d r)
	(while 
		(setq d (tblnext s (null d)))
		(setq r (cons (cdr (assoc 2 d)) r))
	);while
);defun
 
;;;End Coding Here

For example, if you would like a list of all layers in a specific drawing, use this :

(setq all_layers (tablelist "LAYER"))

AutoLisp should return something like this :

("7" "6" "5" "4" "3" "2" "0")

To populate a list box with the key of "selections," use this :

(start_list "selections")
(mapcar 'add_list all_layers)

To get the full path, you append the DWGPREFIX system variable (which stores the path) to the DWGNAME system variable (which stores the file name). Use code such as the following example to retrieve and assign the values of DWGNAME and DWGPREFIX to variables in AutoLISP :

(setq DN (getvar "DWGNAME"))
(setq DP (getvar "DWGPREFIX"))

Use the AutoLISP function (strcat) to concatenate the results and assign them to a variable, for example :

(setq TM (strcat DP DN))

In this example, the variable TM contains the full path including the file name.

Did you know that you can write block comments in your AutoLisp files like this :

;| This is the start of the comments.
   You can carry your comments to multiple lines.
   This will end your comments |;

That little line is the pipe character or vertical bar.

This will display the length of most entities :

;Coding starts here
(defun c:lg ( / x_object x_length)
(vl-load-com)
(setq x_object (entsel))
(setq x_object (vlax-Ename->Vla-Object (car x_object)))
(setq x_length (vlax-curve-getdistatparam x_object 
               (vlax-curve-getendparam x_object )))
(alert (strcat "Length = " (rtos x_length)))
(princ)
);defun
(princ)
;Coding ends here