Subj : Re: String concat problem
To   : netscape.public.mozilla.jseng
From : Brendan Eich
Date : Tue Apr 20 2004 11:37 am

Niklas Lindquist wrote:
> I have created a class exposing a string property. It works like a charm,
> except when it comes to using it to build longer strings.
> In JavaScript:
> s = myobj.name;
> s = 'Pre: ' + myobj.name;
> s = myobj.name.length + ' post';
> all works fine, but:
> s = myobj.name + ' post';
> only returns the name property and doesn't concatenate it with ' post'. I
> can run toLowerCase() and similar functions on my string, so it seems to be
> correct.
> 
> I have initialized my string in the getProperty hook:
> int length = ::strlen(pDoc->getName()) + 1;
> char* buffer = reinterpret_cast<char*>(::JS_malloc(cx, length));

You should let length be strlen() and add 1 here in the malloc call.

> ::strcpy(buffer, pDoc->getName());
> JSString *str = ::JS_NewString(cx, buffer, length);

because you need to pass the length, not the size, here to JS_NewString. 
  What you are doing now wrongly informs the JS engine that the string 
has a NUL included in its characters, at the end.  That crops printing 
in the JS shell and any other 8-bit environment.

/be

> *vp = STRING_TO_JSVAL(str);
> 
> Have I missed something?
> 
>

.