This is a shortcut, it avoid to use a struct to store the int. Sometimes for
an example it is better to have less code, this way you only see the
interesting part. But of course this is not a good example for newbies.
2010/5/19 Brett Nash <n...@nash.id.au>
> On Tue, 18 May 2010 22:01:57 +0200
> Andreas Volz <li...@brachttal.net> wrote:
>
> > Hello,
> >
> > I noticed a problem in the Elementary GenList example code:
> >
> > static Elm_Genlist_Item_Class itc1;
> > char *gl_label_get(const void *data, Evas_Object *obj, const char
> > *part) {
> > char buf[256];
> > snprintf(buf, sizeof(buf), "Item # %i", (int)data);
> > return strdup(buf);
> > }
> >
> > static void
> > gl_sel(void *data, Evas_Object *obj, void *event_info)
> > {
> > printf("sel item data [%p] on genlist obj [%p], item pointer
> > [%p]\n", data, obj, event_info);
> > printf ("data val: %i\n", (int) data);
> > }
> >
> > void
> > test_genlist(void *data, Evas_Object *obj, void *event_info
> > {
> > int i;
> > ...
> >
> > for (i = 0; i < 2000; i++)
> > {
> > gli = elm_genlist_item_append(gl, &itc1,
> > (void *)i/* item data */,
> > NULL/* parent */,
> > ELM_GENLIST_ITEM_NONE,
> > gl_sel/* func */,
> > (void *)(i * 10)/* func data
> > */); ...
> > }
> >
> > While wrapping GenList to C++ I noticed that something really bad
> > happens here. The value of 'i' and 'i*10' is casted into a pointer
> > type and later casted back to int. I'm really sure this code isn't
> > covered by the C standard and not portable in any way. This code
> > needs the int type to have the same size as a pointer type. But there
> > may be architectures/compilers where this isn't the case. And even if
> > this works here it may bring someone to the idea to do the same with
> > other integral types where this won't work for sure. Not a smart idea
> > in a public example...
> >
> > If you think this is correct code and I'm wrong please enlighten
> > me. :-)
>
> It's technically not correct. Yes it hits something undefined in there.
> Practically however it's only a problem if sizeof(int) > sizeof(ptr) or
> some weird platform which doesn't support odd pointers or something
> (cray I's?). Don't think efl runs on any of those platforms ;-)
>
> Pratically it's fine. A slight improvement may be to cast it to an
> intptr_t which will protect it against different size void/int's (And
> will reduce warnings too).
>
> > If not I'll change the example to hold two int arrays in the correct
> > scope and work with pointer type data.
>
> Or do that ;-)
>
>
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>
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--
Regards.
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