Michael Haggerty <mhagger@xxxxxxxxxxxx> writes: > If you pass a newly-initialized or newly-cleared `string_list` to > `for_each_string_list_item()`, then the latter does > > for ( > item = (list)->items; /* note, this is NULL */ > item < (list)->items + (list)->nr; /* note: NULL + 0 */ > ++item) > > Even though this probably works almost everywhere, it is undefined > behavior, and it could plausibly cause highly-optimizing compilers to > misbehave. > ... > It would be a pain to have to change the signature of this macro, and > we'd prefer not to add overhead to each iteration of the loop. So > instead, whenever `list->items` is NULL, initialize `item` to point at > a dummy `string_list_item` created for the purpose. > ... > -#define for_each_string_list_item(item,list) \ > - for (item = (list)->items; item < (list)->items + (list)->nr; ++item) > +extern struct string_list_item dummy_string_list_item; > +#define for_each_string_list_item(item,list) \ > + for (item = (list)->items ? (list)->items : &dummy_string_list_item; \ > + item < (list)->items + (list)->nr; \ > + ++item) Sorry, but I am confused. So when (list)->items is NULL, the loop termination condition that used to be NULL < NULL + 0 that was problematic because NULL + 0 is problematic now becomes &dummy < NULL + 0 in the new code? What made NULL + 0 not problematic now?
