Subj : Re: GetProperty
To   : netscape.public.mozilla.jseng
From : "Jochen Stier" <jstier@cs.uvic.ca>
Date : Wed Feb 11 2004 08:33 am

>Cool -- I am ex-SGI ('85-'92), glad to hear of an
>OpenInventor/SpiderMonkey combo.

He, nice! Then you know what I am up to. I am using the coin3d
implementation, tho. It is the same
Api but different authors...

>You  should instead return JS_NewNumberValue(iContext, lValue, vp).

That is exactly what I needed to know. Thxs

Cheers
Jochen


"Brendan Eich" <brendan@meer.net> wrote in message
news:40298952.6040309@meer.net...
> Brendan Eich wrote:
>
> >> JSBool ScrSFVec3f::JSGetProperty(JSContext* iContext, JSObject*
iObject,
> >> jsval id, jsval *vp)
> >> {
> >>    if (JSVAL_IS_INT (id))
> >>    {
> >>          SoSFVec3f* lVector = (SoSFVec3f*) JS_GetPrivate(iContext,
> >> iObject);
> >>
> >>            static double lValue;
> >>            lValue = lVector->getValue()[JSVAL_TO_INT(id)];
> >>            *vp = DOUBLE_TO_JSVAL(&lValue);
> >>        }
> >>        return JS_TRUE;
> >> }
> >>
> >>
> >> Now, my question is if the Javascript engine makes a copy of the
> >> double, or does it come back to the memory location of lValue
> >> whenever it needs to read the value of the double. This is important
> >> for the following javascript
> >
> >
> > It's important for the above example too -- you're returning the
> > address of a stack temporary that goes out of scope as soon as
> > ScrSFVec3f::JSGetProperty returns!
> >
> > Be careful with pointers (addresses) in C ;-).
>
>
> And I should be careful with my skimming of your code!  Sorry, I missed
> the "static" storage class on double lValue (need my eyes examined).
>
> But my final point stands.  You can't take any old jsdouble address and
> tag it as a jsval and store it in a property or other place known to the
> GC.  Only GC-allocated jsdoubles can be so tagged.  Hope this is all
> clear now.
>
> /be

.