Hi,

How can I use the following c structure from d.

struct Item
{
  int id;
};

struct Group
{
  int i;
  int item_count;
  struct Item items[];
};

tried defining items[] as both "Item[] items" and "Item* items" in d, it compiles okay but gives an error when trying to access it.

Here is the error.
object.Error@(0): Access Violation
----------------
0x00BCA9D1
0x00BC104C
0x00BD01EB
0x00BD0169
0x00BD0000
0x00BCA827
0x74118654 in BaseThreadInitThunk
0x77534B17 in RtlGetAppContainerNamedObjectPath
0x77534AE7 in RtlGetAppContainerNamedObjectPath


Regards,
NewUser

On Friday, 4 May 2018 at 13:02:08 UTC, NewUser wrote:
> How can I use the following c structure from d.
>
> struct Item
> {
>   int id;
> };
>
> struct Group
> {
>   int i;
>   int item_count;
>   struct Item items[];
> };
>
> tried defining items[] as both "Item[] items" and "Item* items" in d, it compiles okay but gives an error when trying to access it.
>
> Here is the error.
> object.Error@(0): Access Violation

The D equivalent is:

struct Item {
    int id;
}

struct Group {
    int i;
    int item_count;
    Item* items;
}

The error message you're getting makes me think items is null. The lack of function names in the stack trace makes it kinda hard to understand exactly what's happening - you can turn that on with -g for DMD. Seeing some of the code that uses these structs might also help.

--
  Simen

On Friday, 4 May 2018 at 13:02:08 UTC, NewUser wrote:
> tried defining items[] as both "Item[] items" and "Item* items" in d, it compiles okay but gives an error when trying to access it.

You were on the right track. D array notation is:

<type>[] <identifier>;

For me this works:

```
struct Item
{
  int id;
};

struct Group
{
  int i;
  int item_count;
  Item[] items;
};

void main()
{
    auto g = Group();
    g.items ~= Item(3);
    assert(g.items[0].id == 3);
}
```

On Friday, 4 May 2018 at 13:21:53 UTC, Timoses wrote:
> On Friday, 4 May 2018 at 13:02:08 UTC, NewUser wrote:
>> tried defining items[] as both "Item[] items" and "Item* items" in d, it compiles okay but gives an error when trying to access it.
>
> You were on the right track. D array notation is:
>
> <type>[] <identifier>;
>
> For me this works:
>
> ```
> struct Item
> {
>   int id;
> };
>
> struct Group
> {
>   int i;
>   int item_count;
>   Item[] items;
> };
>
> void main()
> {
>     auto g = Group();
>     g.items ~= Item(3);
>     assert(g.items[0].id == 3);
> }
> ```

Hi Timoses,

The structure is being returned from c and I'd like use it from d.

What you have work perfectly when assigning from d.


Regards,
NewUser

On Friday, 4 May 2018 at 13:27:03 UTC, NewUser wrote:
> Hi Timoses,
>
> The structure is being returned from c and I'd like use it from d.
>
> What you have work perfectly when assigning from d.
>
>
> Regards,
> NewUser

Then you probably need some `extern(C)` statement introducing the C function and the struct type, right?

You could also try dstep to "translate" the C header file to D:
https://github.com/jacob-carlborg/dstep

On Friday, 4 May 2018 at 14:55:18 UTC, Timoses wrote:
> On Friday, 4 May 2018 at 13:27:03 UTC, NewUser wrote:
>> Hi Timoses,
>>
>> The structure is being returned from c and I'd like use it from d.
>>
>> What you have work perfectly when assigning from d.
>>
>>
>> Regards,
>> NewUser
>
> Then you probably need some `extern(C)` statement introducing the C function and the struct type, right?
>
> You could also try dstep to "translate" the C header file to D:
> https://github.com/jacob-carlborg/dstep

Hi Timoses,

Thanks for the suggestion, i'll try it out.

Regards,
NewUser

On Friday, 4 May 2018 at 13:02:08 UTC, NewUser wrote:
> How can I use the following c structure from d.
>
> struct Item
> {
>   int id;
> };
>
> struct Group
> {
>   int i;
>   int item_count;
>   struct Item items[];
> };
>
> tried defining items[] as both "Item[] items" and "Item* items" in d, it compiles okay but gives an error when trying to access it.
>
> Here is the error.
> object.Error@(0): Access Violation

In the C code, the elements of `items` are directly part of the struct. There is no indirection. D doesn't have dedicated syntax for this, but you can hint at it with a zero-sized array:

struct Group
{
    int i;
    int item_count;
    Item[0] items;
}

Then access an item with `group.items.ptr[index]`.

On Friday, 4 May 2018 at 15:37:28 UTC, ag0aep6g wrote:
> On Friday, 4 May 2018 at 13:02:08 UTC, NewUser wrote:
>> How can I use the following c structure from d.
>>
>> struct Item
>> {
>>   int id;
>> };
>>
>> struct Group
>> {
>>   int i;
>>   int item_count;
>>   struct Item items[];
>> };
>>
>> tried defining items[] as both "Item[] items" and "Item* items" in d, it compiles okay but gives an error when trying to access it.
>>
>> Here is the error.
>> object.Error@(0): Access Violation
>
> In the C code, the elements of `items` are directly part of the struct. There is no indirection. D doesn't have dedicated syntax for this, but you can hint at it with a zero-sized array:
>
> struct Group
> {
>     int i;
>     int item_count;
>     Item[0] items;
> }
>
> Then access an item with `group.items.ptr[index]`.

Hi ag0aep6g,

Thanks a lot for that.

I should have thought of that (i would still have missed the .ptr part), the old c syntax for the same thing used to be "Item items[0]".

Thanks,
NewUser