Am 12.07.19 um 18:44 schrieb Junio C Hamano:
> Johannes Sixt <j...@kdbg.org> writes:
>
>> Am 12.07.19 um 00:03 schrieb Ramsay Jones:
>>> diff --git a/range-diff.c b/range-diff.c
>>> index ba1e9a4265..0f24a4ad12 100644
>>> --- a/range-diff.c
>>> +++ b/range-diff.c
>>> @@ -102,7 +102,7 @@ static int read_patches(const char *range, struct
>>> string_list *list)
>>> }
>>>
>>> if (starts_with(line, "diff --git")) {
>>> - struct patch patch = { 0 };
>>> + struct patch patch = { NULL };
>>
>> There is nothing wrong with 0 here. IMHO, zero-initialization should
>> *always* be written as = { 0 } and nothing else. Changing 0 to NULL to
>> pacify sparse encourages a wrong style.
>
> Hmm, care to elaborate a bit? Certainly, we have a clear preference
> between these two:
>
> struct patch patch;
> patch.new_name = 0;
> patch.new_name = NULL;
>
> where the "char *new_name" field is the first one in the structure.
> We always try to write the latter, even though we know they ought to
> be equivalent to the language lawyers.
I'm not questioning this case; the latter form is clearly preferable.
Using only = { 0 } for zero-initialization makes the code immune to
rearrangements of the struct members. That is not the case with = { NULL
} because it requires that the first member is a pointer; if
rearrangement makes the first member a non-pointer, the initializations
must be adjusted.
On the other hand, I'm not arguing that
struct string_list dup_it = { NULL, 0, 0, 1, NULL };
should be written as
struct string_list dup_it = { 0, 0, 0, 1, 0 };
I'm only complaining about the single-initializer = { 0 } "please
initialize this whole struct with zero values" form.
> Is the reason why you say 0 is fine here because we consider
>
> struct patch patch, *dpatch;
> memset(&patch, 0, sizeof(patch));
> dpatch = xcalloc(1, sizeof(patch));
>
> are perfectly good way to trivially iniitialize an instance of the
> struct?
Absolutely not. Both forms are evildoing as far as struct initialization
is concerned because they ignore the types of the members. The memset
form should always be replaced by = { 0 }. The correct replacement for
the xcalloc form would be
struct patch zero = { 0 };
struct patch *dpatch = xmalloc(sizeof(*dpatch));
*dpatch = zero;
but I do understand that this transformation is unacceptably verbose.
> Do we want to talk to sparse folks about this?
I've no idea which camp they are in. How would they respond to an
exceptional case that is also very much a matter of taste?
-- Hannes
