Subj : Re: Returning integers from custom functions.
To   : Frank Schroeder <frank_schroeder@hotmail.com>
From : Brendan Eich <brendan@meer.net>
Date : Fri Jul 18 2003 07:11 pm

Frank Schroeder wrote:

>I've implemented a custom object with a couple of functions that are
>supposed to return an integer value:
>
>
>static JSBool Input_Width(JSContext *cx, JSObject *obj, uintN argc, jsval
>*argv, jsval *rval)
>{
> *rval=STRING_TO_JSVAL(JS_NewStringCopyZ(cx, "53"));
>
> return JS_TRUE;
>}
>  
>

Don't return a string if you want to return a number.

Also, if you do call JS_NewStringCopyZ, check for failure (null return 
value).

>When I call the function and perform an addition,
>
>Response.Write(Input.Width()+1);
>
>the result is 531, so it's concatenating the strings. Weird enough,
>subtraction etc. is working fine, i.e.
>
>Response.Write(Input.Width()-1);
>
>comes out as 52.
>

That's how the language works, and always has.

>What can I do to have the return value correcly treated as an integer/double
>and perform an integer addition? I've tried replacing the STRING_TO_JSVAL
>with DOUBLE_TO_JSVAL, to no avail.
>

You realize DOUBLE_TO_JSVAL takes a pointer to a jsdouble that was 
allocated from the GC heap?

Sterling suggested:

JS_NewNumberValue(cx,53,&rval);

which works fine, but if you know you want 53, just

rval = INT_TO_JSVAL(53);

works the same and is faster, infallible, and less code.

/be

.