Subj : Re: how to make C functions return array to js?
To   : Oyku Gencay <oyku@sbt.com.tr>
From : Brendan Eich <brendan@meer.net>
Date : Wed Mar 17 2004 10:02 am

Oyku Gencay wrote:
> Hi folks,
> 
> How can I return an array to javascript from a C function? I have a 
> native C function which returns an array.  When I run this I get a 
> segfault.

Where?  What stack?

> The function code is;
> 
> static JSBool
> TestingArraysAsReturn(JSContext *cx, JSObject *obj, uintN argc,
>     jsval *argv, jsval *rval) {
> 
> JSObject *js_array ;
> js_array = JS_NewArrayObject(cx,0,NULL);
> for (i = 1 ; i <= 5 ; ++i) {
>     jsval *js;
>     js = STRING_TO_JSVAL(JS_NewStringCopyZ(cx, "testing"));

Bug: you are assigning a jsval to a jsval* here, surely your compiler 
warned you?

You want jsval v = STRING_TO_JSVAL(str); where str is set to the result 
of JS_NewStringCopyZ, and you test that result against null first, 
returning false to handle out-of-memory errors.

>     JS_SetElement(cx,js_array,i,js);

So you want &v, not js, here.

> }
> *rval = OBJECT_TO_JSVAL(js_array);
> return JS_TRUE;
> }

Please also read http://www.mozilla.org/js/spidermonkey/gctips.html, 
note the need to root as you go.  Storing *rval late is not good -- what 
if the GC ran from one of the JS_NewStringCopyZ calls?

/be

.