Passing static arrays to C

[Jacob Carlborg]

On 2012-10-24 09:54, Jakob Bornecrantz wrote:
> Hey everybody.
>
> How are you supposed to pass static arrays to C functions? I'm asking
> because I'm getting conflicting info from how DMD works and on IRC.
>
> The below example prints:
> test1 0x7fff857c1db0
> test2 0x7fff857c1db0
> test3 (nil)
> test4 0x7fff857c1db0
>
>
> D:
> void main()
> {
>          float[3] arr;
>          test1(arr);
>          test2(&arr[0]);
>          test3(0, arr);
>          test4(0, &arr[0]);
> }
>
> extern(C):
> void test1(float[3] arr);
> void test2(float *arr);
> void test3(int, float[3] arr);
> void test4(int, float *arr);
>
>
> C:
> #include <stdio.h>
>
> void test1(float arr[3]) { printf("test1 %p\n", &arr[0]); }
> void test2(float arr[3]) { printf("test2 %p\n", &arr[0]); }
> void test3(int anything, float arr[3]) { printf("test3 %p\n", &arr[0]); }
> void test4(int anything, float arr[3]) { printf("test4 %p\n", &arr[0]); }

That seems weird. Since static arrays are passed by value in D you need 
to send a reference:

extern (C) void test1(ref float[3] arr);

float[3] arr;
test1(arr);

BTW, do not ever use "&arr[0]", use "arr.ptr" instead to get the pointer 
of the array.

http://dlang.org/interfaceToC.html

Search for "Passing D Array Arguments to C Functions".

-- 
/Jacob Carlborg