Though AutoLISP routines should work just fine on AutoCAD 2010, any application using ObjectARX for previous versions of AutoCAD will have to be recompiled and possibly changed. AutoCAD 2010 is not binary compatible with previous releases.

Dimensional constraints do not behave as associative dimensions when opened in previous versions of AutoCAD. You will need to reassociate dimensions using the Dimreassociate command.

You can change the multiline style that is the current default by typing CMLSTYLE at the command prompt. When you press Enter, the current multiline style is displayed at the command prompt. Type in the name of the style you want to be current, and press Enter. Note that the style must be loaded in the drawing in order to be the current style. Unfortunately, there is no way to view the available styles from the command line.

Though not the usual kind of bug associated with AutoCAD, viruses can inflict themselves on the unwary user. According to Autodesk, the two main types of viruses that can affect AutoCAD are:

• VBA macros embedded in drawing files
• AutoLISP routines that run automatically when a drawing is opened

Once a VBA macro is embedded in a drawing, it can become active when a drawing is loaded and affect any computer on which it is active. VBA macros may manipulate drawing data and access your hard drive and registry.

AutoLISP-based viruses are usually transmitted via one of the AutoLISP files that run automatically:

• acad200xdoc.lsp: Autodesk-created file that runs every time a drawing is opened
• acad200x.lsp: Autodesk-created file that runs when AutoCAD starts up
• acaddoc.lsp: User-created file that runs every time a drawing is opened
• acad.lsp: File that runs when AutoCAD starts up

According to Autodesk, what typically happens is that you receive a zip file or archive that contains drawing files, one of which starts AutoLISP files. When you extract the files to a folder and load a drawing, the included AutoLISP file is also loaded. Once loaded, it runs. AutoLISP has the ability to execute AutoCAD commands, run VBA macros, access your Windows registry, execute Windows applications, and create, modify, and delete files on your computer.

Here are some tips to help avoid infection:

• Keep your antivirus software up to date. Most programs are aware of the most common AutoLISP viruses and will quarantine the files when detected.
• Check the contents of zip files and archives (.RAR, etc.) before you unzip them. Be suspicious of any files that contain EXE, ARX (ObjectARX), VBA, or AutoLISP files.
• Never run an unknown AutoLISP file or VBA macro without inspecting it first. Do this by opening the file in Notepad or the VBA Editor and making sure the command sequence is what was advertised.
• Make sure you have enabled the macro virus protection in AutoCAD. AutoCAD will warn you when you open a drawing or project file that contains embedded macros and allow you to disable them before they can run. Start the VBArun command, select the Options button, and make sure the box for Enable macro virus protection is checked.

Caption: Enable macro virus protection can be turned on in the VBArun command’s Options dialog box.

Here’s how to create a dimension with two lines of text. First, make sure the Properties window is open. Select your dimension. In the Properties window under Text, find the Text Override window.

Caption: Properties window for the rectangle’s top dimension.

Here you enter your desired dimension text. The actual dimension value is represented by a pair of pointy brackets: <>. The pointy brackets ensure that the dimension remains associative. At the point where you want a second line to start, insert \X (backslash X). If you want even more lines of text, insert \P wherever you want a line break.

Caption: The string shown in the Text override box at left yields the results on the right.

Caption: Note that you can position the dimension value anywhere amid your text.

The DYNMODE system variable controls the dynamic input settings we discussed previously. Its settings are as follows:

0 =  All Dynamic Input features are off
1 = Pointer input is on
2 = Dimensional input is on
3 = Both Pointer and Dimensional input are on

When DYNMODE is set to a negative value, Dynamic Input is off, but the setting is stored. When you press the Dyn button in the status bar, DYNMODE is set to the corresponding positive value.

When Dimensional input is on (DYNMODE = 2 or 3), you can select multiple objects that share a common grip and press the Tab key to cycle through all of the dimensions for each selected object.

When Pointer input (DYNMODE = 1 or 3) is on, you can use the left pointy bracket (<) or the comma (<) instead of the Tab key to display an additional input field.

When Dynamic Prompts are turned on (DYNPROMPT = 1), they will display when DYNMODE = 1, 2, or 3. They will not display when DYNMODE = 0, regardless of the DYNPROMPT setting.

If you use AutoCAD 2006, turn Dynamic Input off before you use the Array command. Otherwise, when you use the Array command with the Polar option and then preview the results, the dynamic input options will display. When you finish the command, the options will remain in your drawing as semitransparent options that cannot be selected or deleted. The problem is fixed in AutoCAD 2007.