In the previous post about Startup Lisp Functions, the special (S::STARTUP) function was mentioned. Startup lisp code is loaded before the drawing is initialized, but you cannot call the (COMMAND) function until after the drawing is initialized. The solution is to place your (COMMAND) calls inside the (S::STARTUP) function.
If you have lisp routines that you want to make available in each drawing session, forget the "Startup Suite" and load them using the "acaddoc.lsp" file. "acaddoc.lsp" is not included with AutoCAD, you create it yourself. But it is nothing more than a plain lisp file, except that the first one found at drawing startup (just put it in your support file search path), is loaded automatically each time a drawing is opened.
Here is a simple example of how to read a TXT file into lisp and then do something with the contents. In this example, the TXT file contains coordinates, and the code will draw either points or lines.
One thing to keep in mind. Most times when you open a file for read or write, you should open the file, perform the entire operation, then close the file. Keep the code to a minimum while the file is open. This way if you run into an unhandled error, the file isn't stuck open, and in the case of shared files, you are not locking the file for an extended amount if time.
If you program with autolisp, you have probably used the command function at some point, probably to construct drawing entities. There is certainly nothing wrong with that. However, if you are working on a large program that constructs a lot of drawing entities, you may have noticed that the command function runs pretty slow.
I put together some tests to compare the (command) function to two other methods of entity creation, (entmake) and (vla-add...). The test constructs 1,999 line entities using various methods.
Here is an example of creating a TABLE entity using lisp. This example also creates some FIELDS using lisp.
This routine allows the user to select closed polylines, and it will create a TABLE with two columns. One containing the area, and the other containing the ObjectID. The last row totals up the area. You could easily adapt this to show the layer, color or any other property.
If you are planning on upgrading to AutoCAD 2008 32-bit, and you have existing LISP, VBA, or ARX programs, will they work? Generally speaking, yes. You may have to make a minor adjustment to your code, but for the most part there shouldn't be any problems.
If you are planning on upgrading to AutoCAD 2008 64-bit, then you may have some decisions to make and/or work to do...
Have you ever set a system variable and then you are working along and that sysvar is changed to a different value? Many people will ask how or why it "changed itself", which obviously it can't do. Of course what is really going on is a program, whether it be an internally defined command, or a lisp/VBA/ARX routine, has changed it.