g_list_previous() / g_list_next()

[Danek Duvall <duvall lorien emufarm org>]

Using Sun's C compiler (WorkShop 5.0), I get a load of errors compiling
xmms (bear with me a moment).  Most of these errors look like the
following:

    "util.c", line 381: non-unique member requires struct/union pointer: data
    "util.c", line 381: left operand of "->" must be pointer to struct/union

Line 381 is:

    list->data = g_list_next(list)->data;

I've been patching each individual problem line by casting the result of
g_list_next (or _previous) to a GList *.  Thus:

    list->data = ((GList *)g_list_next(list))->data;

However, I noticed that it is possible to correct the problem by patching
glib.h instead to do the cast ahead of time:

    --- /export/include/glib.h      Tue Jun 29 11:55:23 1999
    +++ glib.h      Sun Jun 18 20:47:12 2000
    @@ -894,8 +894,8 @@
				     GCompareFunc    compare_func);
     gpointer g_list_nth_data       (GList          *list,
				     guint           n);
    -#define g_list_previous(list)  ((list) ? (((GList *)(list))->prev) : NULL)
    -#define g_list_next(list)      ((list) ? (((GList *)(list))->next) : NULL)
    +#define g_list_previous(list)  ((GList *)((list) ? (((GList *)(list))->prev) : NULL))
    +#define g_list_next(list)      ((GList *)((list) ? (((GList *)(list))->next) : NULL))
     
     
     /* Singly linked lists

In some sense, this is probably correct, as the developer expects a GList *
in return (and that would happen if these were functions), not sometimes a
GList * and sometimes a void * (or however else NULL is implemented).

The patch was made to 1.2.3, but should apply to 1.2.8 as well.

Thanks for your consideration,
Danek