About Variables (AutoLISP)

Variables are used to store a value or list of values in memory.

The data type of a variable is determined when a value is assigned. Variables retain their value until a new value is assigned or the variable goes out of scope. The scope of a variable can either be global or local. Global variables are accessible by any AutoLISP program that is loaded into a drawing, while local variables are only available within a specific function or command. You use the AutoLISP setq function to assign values to variables.

The syntax of the setq function is as follows:

(setq variable_name1 value1 [variable_name2 value2 ...])

The setq function assigns the specified value to the variable name given, and returns the last assigned value as its function result. The following example creates two variables: val and abc. val is assigned the value of 3, while abc is assigned the value of 3.875.

(setq val 3 abc 3.875)
3.875

The following example creates a variable named layr and assigns it the value of “EXTERIOR-WALLS”.

(setq layr "EXTERIOR-WALLS")
"EXTERIOR-WALLS"

Using a Variable with a Function

Once a value is assigned to a variable, it can be used in an expression as the value for an argument of a function. The following uses two of the previously created variables in a few AutoLISP expressions to create a layer and draw a line with a specific length at 0 degrees.

(command "_.-layer" "_make" layr "")
(command "_.line" PAUSE (strcat "@" (itoa val) "<0") "")

Checking the Value of a Variable

You can use the following methods to determine the current value of a variable:

• At the AutoCAD Command prompt, add an ! (exclamation point) in front of the variable and press Enter.

  Command: (setq val 3 abc 3.875)

  3.875

  Command: !val

  3

• At the Visual LISP Console Window prompt, enter the name of the variable and press Enter. (Windows only).

  _$ (setq val 3 abc 3.875)

  3.875

  _$ val

  3

• At the AutoCAD Command prompt or Visual LISP Console Window prompt (Windows only), or in an AutoLISP program, create an expression that uses the princ function and pass it the name of the variable. You should also follow the first expression with a second expression that uses the princ function, but do not pass it an argument to suppress the return value of the first princ function.

  Command: (setq val 3 abc 3.875)

  3.875

  Command: (princ val)(princ)

  3

  Note: If you do not add the second expression in the above example, a value of 33 appears to be returned. The first 3 is the desired output of the princ function, while the second 3 is the result of the value returned by the princ function. Remember that AutoLISP returns the value of the last function evaluated. In the previous example, no value is returned by the second princ because no argument was provided.