Re: FFI arg_types for C array

[Myles English]

Hi Nala,

On Tue, 10 Mar 2020, 18:50 Nala Ginrut, <address@hidden> wrote:

> If I understand your question correctly,  the arg_type should be (list int
> '*)
>
> On Tue, Mar 10, 2020 at 10:25 PM Myles English <address@hidden>
> wrote:
>
I am trying to call a C function with this signature from Guile:
>
>>
>> void the_test(int n, const int the_array[]);
>>
>> in pointer->procedure what should arg_types be?
>>
>
Thank you for reply, it does indeed answer my original question.  Now, how
do I call the guile procedure to use the C function?  I thought this might
work but it doesn't:

In file main.scm:

(use-modules (system foreign)
                         (rnrs bytevectors))

(define libarray (dynamic-link "/path/to/libarray.so"))

(define the-test
  (pointer->procedure void
    (dynamic-func "the_test" libarray)
    (list int '*)))

(define (call-the-test)
  (let* ((bv  (u8-list->bytevector '(1 2 3 4 5 6 7 8 9)))
(bv_p (bytevector->pointer bv)))
    (display bv) (newline)
    (the-test 9 bv_p)))

(call-the-test)

In file array.c:

#include <stdio.h>
void the_test(int n, const int the_array[])
{
  int i, k;
  for (k = 1; k <= n; k++)
    {
      i = the_array[k];
      printf("the_array [%d] = %d\n", k, i);
    }
  return;
}

compiled with:

gcc -c -Wall -fpic array.c && gcc -shared -o libarray.so array.o

This is the result of calling the guile module, (I was hoping to get the
numbers 1 to 9):

$ guile main.scm
  #vu8(1 2 3 4 5 6 7 8 9)
the_array [1] = 134678021
the_array [2] = 9
the_array [3] = 0
the_array [4] = 0
the_array [5] = 0
the_array [6] = 0
the_array [7] = 0
the_array [8] = 27
the_array [9] = 0

In addition to the main question above, the C function expects a 1-based
index for the array, how would the guile procedure accommodate this?

Thanks,
Myles

>