On 08/08/2012 07:12 AM, Alexandr Druzhinin wrote:
> 08.08.2012 16:29, bearophile пишет:
>>> That C code doesn't look correct, because the given data contains no
>>> pointers.
>>
>> But this C code compiles:
>>
>>
>> void foo(const void** data) {}
>> int data[2][3];
>> int main() {
>> foo(data);
>> return 0;
>> }
gcc does not accept that code:
deneme.c:18920: error: passing argument 1 of ‘foo’ from incompatible
pointer type
deneme.c:18914: note: expected ‘const void **’ but argument is of type
‘int (*)[3]’
> As I know in C an array is equal to pointer,
In C and C++, an Array is automatically converted to a pointer to its
first element.
> so array of array == array
> of pointers == pointer to pointer == pointer to array. Correct me if I'm
> wrong.
>
> I'm trying to use OpenGL function glMultiDrawElements. It has signature:
> void glMultiDrawElements(
> enum mode,
> sizei *count,
> enum type,
> void **indices,
> sizei primcount
> );
I looked at its online documentation: count is also an array that tells
the lengths of individual rows of indices, right? So in reality the data
is a dynamic ragged array? (I've never used that function before.)
> If I declare indices like
> uint[][] indices;
That's a slice of uint slices. Completely different memory layout than
static arrays.
In any case, I am pretty sure that what you need is the .ptr property of
D arrays. You will have to make the 'indices' parameter dynamically by
calling .ptr on the slices.
> then code compiles but doesn't work (but it works in C). If I do as I
> described in the first post - it works in D. And I'd like to understand
> the reason of it. I think the reason is difference tween C array and D
> array, but I'm not sure.
>
> p.s. example of real code is too large to paste
I've started writing the following but I don't know how you are calling
the function. Can you get this to do what you expect in C:
// WARNING: THIS C CODE DOES NOT COMPILE.
#include <stdio.h>
typedef size_t sizei;
void glMultiDrawElements(
/* enum mode,*/
sizei *count,
/* enum type,*/
void **indices,
sizei primcount)
{
for (size_t i = 0; i != primcount; ++i) {
for (size_t j = 0; j != count[i]; ++j) {
printf(" %d", indices[i][j]);
}
printf("\n");
}
}
int main()
{
/* Normally, the count array would be generated dynamically. */
int counts[4] = { 3, 3, 3, 3 };
int data[4][3];
data[0][0] = 42;
data[2][2] = 43;
glMultiDrawElements(counts, data, 4);
}
Ali
--
D Programming Language Tutorial: http://ddili.org/ders/d.en/index.html
