Empty selection set - how to process (sslenght ...)?

[jlc.pub]

Hi,

I'm trying to do a very simple lisp which ask the user which layer he wants to clean and delete all items on it.

The layer selected by the user is named "folasup" and I make a selection set by :

(setq sel (ssget "x" (list (cons '8 Folasup))))

Then I try this condition :

(if (> (sslength sel) 0)

My problem is when there is nothing in the selection set... in this case the watch shows me that the content of "sslength sel" is <***ERROR***>.

I don't know how to consider this case.

Could you help me please ?

[cadffm · Accepted solution]

(If (setq sel (ssget "x" (list (cons '8 Folasup))))

(Progn Mystuff)

)

OR

(And

(setq sel (ssget "x" (list (cons '8 Folasup))))

(Mystuff)

)

[ronjonp · Accepted solution]

Here's another:

(if (setq sel (ssget "_X" '((8 . "Folasup"))))
  (foreach x (mapcar 'cadr (ssnamex sel)) (entdel x))
)

[dlanorh]

---

@jlc.pub wrote:

Hi,

I'm trying to do a very simple lisp which ask the user which layer he wants to clean and delete all items on it.

The layer selected by the user is named "folasup" and I make a selection set by :

(setq sel (ssget "x" (list (cons '8 Folasup))))

Then I try this condition :

(if (> (sslength sel) 0)

My problem is when there is nothing in the selection set... in this case the watch shows me that the content of "sslength sel" is <***ERROR***>.

I don't know how to consider this case.

Could you help me please ?

---

(setq sel (ssget ....))

(if sel
  (progn
    ;process selection set
  );end_progn
  (progn
    (alert "Nothing Selected") or whatever
  );end_progn
);end_if

or

(setq sel (ssget ....))

(cond (sel
        ;process selection set
       )
       (t
         (alert "Nothing Selected") or whatever
        )
);end_cond

[jlc.pub]

So fast !

Thanks for your quick reply ! I've tried the first method, it's work perfectly 😁

Thanks

[ВeekeeCZ]

---

@jlc.pub wrote:

...

(setq sel (ssget "x" (list (cons '8 Folasup))))

Then I try this condition :

(if (> (sslength sel) 0)

My problem is when there is nothing in the selection set... in this case the watch shows me that the content of "sslength sel" is <***ERROR***>.

..

---

This is bad wording. Your issue isn't "nothing in the ss". It would imply that ss exists but it's empty. But in your case, ss simply does not exist. If comes to selection sets, its really important to understand the difference whether it exists or not and if yes, then whether is empty or not.

If you do something like this: (setq ss (ssadd)) 

Now ss is an empty selection set. It means 

- it exists.... (not ss) returns nil

- but it's empty.... (sslength ss) returns 0.

HTH