Lisp (well AutoLisp) works the other way round. Instead of telling the function that its parameter is referencing something from outside, you tell the place where you call the function that the argument you're sending it needs to be "by reference". In Lisp this is rather referred to as sending the symbol name instead of the symbol's value. Also the function needs to work on the assumption (or test for) that the parameter is a symbol name instead of a value.
So when writing something like this in Lisp, you'd have done something like:
(defun GetPointZCoord
(Pt ZCoord
/ Coord
) (and Pt
;Check if point object (setq Coord
(vlax-get Pt 'Coordinates
)) ;And get coordinates (= (type ZCoord
) 'Sym
) ;Check if ZCoord is passed in as a symbol name (set ZCoord
(nth 2 Coord
)) ;Check if Z can be set into symbol parameter )
)
Note when setting the value to the ZCoord parameter it's first checked to see if it is just a symbol name. Then it uses SET instead of SETQ, i.e. use the symbol name inside the variable instead of quoting the variable's name and then setting that. Now when calling that function, you need to quote the "variable" passed in as the ZCoord argument - i.e. you're quoting it outside the function which is going to set it.
Here's a sample from ACad's command-line:
Command: (GetPointZCoord (vlax-ename->vla-object (car (entsel))) 'Z)
Select object: T
Command: !Z
2000.0Notice the ' prefix to Z - short hand for writing (quote Z).
Now, you're working from the DotNet side. If what you're after is to set the argument in Lisp from within DotNet - that's a whole new ballgame. Unfortunately ADesk's interaction between DotNet and Lisp do not cater for these things - all arguments passed in to DotNet is converted to a ResultBuffer list and is always only passed in as ByValue. Not to mention, DotNet doesn't accept vla-objects as arguments to its LispFunction methods - you'd simply need to send it the ename as obtained from (car (ensel)) instead.
To get around this issue though you can "simulate" something like a ByRef parameter, by expecting a string naming the symbol in the ZCoord parameter's place. This you do using the document object's SetLispSymbol method - see an example use here:
http://adndevblog.typepad.com/autocad/2014/08/set-or-get-lisp-symbol-in-net.htmlEdit: Sorry I see you're making Com-interop. Well perhaps this works, just call that function in the same way you'd call it if it was written in Lisp as above - i.e. prefix the Z value with a quote. E.g. that's how you'd call the standard ActiveX GetBoundingBox method:
After which MinCoord would contain the "bottom left 3d point as a safearray of variants, as would the MaxCoord contain that of the top-right.
If the same happens for your custom Com exported function I've never really tested. Perhaps you've found a better way to get this working than that convoluted SetLispSymbol idea.
