Variables stored in drawing file

I thought I heard someone here discussing how acad has the ability to store
(6?) variables in the drawing file that survive the drawing session.

Anyone recall that/know about how it's done?

 

HiHO;
Look at USER**, they are real, integer, and string.

 

Thanks. That's what I was looking for.

Has anyone ever used these things?
Are there any pitfalls in using them for storage of data between sessions?
Will any native functions try to overwrite them should you assign a value to
them?
What the hell are they for?

I started thinking that they might be of use to the guy in a another thread
who
wanted a prompt to pop up after an issued drawing is revised so that the
operator will remember to fill out the revision block.

 

They're provided, as the name implies, for the USER to store up to five
integers, five reals and five strings for whatever purpose the USER may
wish. USERI1-5 and USERR1-5 are saved in the .dwg file, so they may be
carried over from session to session. USERS1-5 are *not* saved, which makes
them of little use to most folks.

The problem with these variables is that they may be also used
indiscriminately by anyone who writes customization for AutoCAD, which means
the USER runs the risk of losing his settings if he runs LISP, VBA, or ARX
routines written by someone else. Good code intended for distribution to
others should *never* use these values for that reason.

Of course, users who use code by others also tend to avoid them because they
may get changed by badly written third-party code ... so without some fairly
strict controls, USERI1-5, USERR1-5 and USERS1-5 are really of limited
practical use.

For storing really "permanent" data in a .dwg file, custom dictinaries are
much more practical, although they require a bit more code to create and
access.
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Thanks Paul, you've confirmed most of my immediate fears about these guys.
One thing
still strikes me as curious: With the ability to assign any variable at the
command line, why did Adesk think someone *needed*
USERS1-5? In the case of the numeric ones, the value persistence is
obviously of some use to
"remember" something from one session to another.

Has anyone ever come across code that re-assigns these variables?
I've just done a quick text search and not one lisp in my 'collection'
contains
any reference to these variables.

 

In the early days (1980's) I did run across a couple of quasi-commercial
packages that used USERRx and USERIx to keep track of things. I've been
known to use them myself (but not recently) to keep track of things like
whether or not a drawing was intended to be plotted in a particular format,
or in the pre-paper space days of things like plotting scales. Today, like
most folks, I ignore them completely, and I haven't seen any decent
third-party stuff in years that attempts to use them.

And, no, I have never understood why USERSx with their limitations were ever
introduced. Were the USERxx variables available in LT (they are NOT,
however) I could see where they might provide a poor-man's substitute for
LISP variables and/or Dictionaries.
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