static init c struct with array filed
```c
struct Test {
int32_t a;
}
struct Test2 {
int32_t a;
Test arr[];
}
```
I need static const init Test2, then pass it to c library
late(third library, can not change the type def).
I am not sure how to do it in D.
Re: static init c struct with array filed
On Wednesday, 16 March 2022 at 07:27:06 UTC, test wrote:
```c
struct Test {
int32_t a;
}
struct Test2 {
int32_t a;
Test arr[];
}
```
I need static const init Test2, then pass it to c library
late(third library, can not change the type def).
I am not sure how to do it in D.
```d
extern(C) struct Test {
int a;
}
extern(C) struct Test2 {
int a;
Test* arr;
}
static const Test2 t2 = Test2(2, null);
void main(){
to_c_library(&t2);
to_c_library(new Test2(2, null));
Test2 local;
to_c_library(&local);
}
```
assuming the c library takes by reference
Re: static init c struct with array filed
On Wednesday, 16 March 2022 at 11:27:20 UTC, user1234 wrote: assuming the c library takes by reference My experience all arrays are effectively just pointers, and the brackets/length is only really applicable to stack allocated fixed length allocations. In my own C projects i always used pointers to pass arrays around. There's also static construction, though i don't see how that improves anything https://dlang.org/spec/module.html#staticorder
Re: static init c struct with array filed
On Wednesday, 16 March 2022 at 14:42:02 UTC, Era Scarecrow wrote: On Wednesday, 16 March 2022 at 11:27:20 UTC, user1234 wrote: assuming the c library takes by reference My experience all arrays are effectively just pointers I meant the function that takes the Test2 as parameter, but to be honest I dont get exactly what does OP want actually... that's true that passing a Test2 is somewhat strange as there's no info for the array length.
Re: static init c struct with array filed
On 3/16/22 10:03, user1234 wrote:
> On Wednesday, 16 March 2022 at 14:42:02 UTC, Era Scarecrow wrote:
>> On Wednesday, 16 March 2022 at 11:27:20 UTC, user1234 wrote:
>>> assuming the c library takes by reference
>>
>> My experience all arrays are effectively just pointers
>
> I meant the function that takes the Test2 as parameter, but to be honest
> I dont get exactly what does OP want actually...
They want to pass Test2 to C and be able to use it. D ABI defines arrays
(slices) as a pair of size_t and a pointer:
https://dlang.org/spec/abi.html#arrays
I haven't passed such a struct to C but I believe the equivalent C
struct can assume there are the following members in place of the array:
struct Test2 {
int32_t a;
size_t length;
Test * ptr;
}
However, the lifetime of ptr must be ensured on the D side because
utless there is a reference to it on the D side, the GC can free the
memory at any time and C side may access invalid memory.
That is explained here:
https://dlang.org/spec/interfaceToC.html#storage_allocation
Ali
Re: static init c struct with array filed
On Wednesday, 16 March 2022 at 07:27:06 UTC, test wrote:
```c
struct Test {
int32_t a;
}
struct Test2 {
int32_t a;
Test arr[];
}
```
I need static const init Test2, then pass it to c library
late(third library, can not change the type def).
Any time you see a '[]' in C, the equivalent declaration in D has
to be a pointer. Like Ali said, D's arrays are a pointer and
length pair, so declaring the declaration of the `arr` member
will not match the declaration on the C side.
Since you say you can't change the declaration on the C side,
user1234's answer is the direction you want to go (though you
don't need the `extern(C)` on the structs).
Re: static init c struct with array filed
On Thursday, 17 March 2022 at 00:16:39 UTC, Mike Parker wrote:
On Wednesday, 16 March 2022 at 07:27:06 UTC, test wrote:
```c
struct Test {
int32_t a;
}
struct Test2 {
int32_t a;
Test arr[];
}
```
I need static const init Test2, then pass it to c library
late(third library, can not change the type def).
Any time you see a '[]' in C, the equivalent declaration in D
has to be a pointer.
Not always with structs... if it has a fixed size or an
initializer in C, then you need to match the size in D.
Otherwise yeah use the pointer.
