----Original Message----
>From: [EMAIL PROTECTED]
>Sent: 19 September 2005 12:09
> "Dave Korn" writes:
>
>> ----Original Message----
>>> From: Richard Henderson
>>> Sent: 19 September 2005 11:26
>>> In the case of the (fake) flexible array member, you do not know
>>> how large the object allocated from malloc was unless you can
>>> track down the actual malloc call.
>>
>> Do you suppose the idiom is common enough that VRP could special-case
>> "arrays of size 1 at the end of a struct" ?
>
> it could be array of size 2, 3, 4, 5, ...
I've seen this trick used again and again and again, and *I* haven't
_ever_ seen anyone use anything except an array size of [1] in this place.
That is to say, I've seen a lot of code that says (to start with your
example):
<-------------------------------------
typedef struct {
int data[1];
} foo;
foo* p = (foo *) malloc (sizeof (foo) + N * sizeof (int));
-------------------------------------
[dk note: I would expect to see (N-1) * sizeof (int) here more usually.
well, either that, or I would expect the comment to read 'enough room for
N+1 ints'.]
-------------------------------------
// there are enough room for N ints, and the store is properly
// aligned.
for (int i = 0; i < N; ++i)
p->data[i] = frobnicate (N, i);
------------------------------------->
but I have never, never, ever seen code that says:
<-------------------------------------
typedef struct {
int data[3];
} foo;
foo* p = (foo *) malloc (sizeof (foo) + (N-3) * sizeof (int));
// there are enough room for N ints, and the store is properly
// aligned.
for (int i = 0; i < N; ++i)
p->data[i] = frobnicate (N, i);
------------------------------------->
Have you?
cheers,
DaveK
--
Can't think of a witty .sigline today....
