Re: how to access c-array member in c-structure?

[Park SungMin]

>> If I understood Park SungMin right, the problem is rather with the
>> representation of a huge array as a list?

> 

correct! (sorry..my poor english)

I think huge c-array should be representation as bytevector or pointer object.

(define type (list int (make-list 10 int)))

(define struct (make-c-struct type (list 42 (make-list 10 42))))

(parse-c-struct struct (list int '*))
=> (42 #<pointer 0x2a0000002a>)

but….when i access to that pointer object
(pointer->bytevector (cadr (parse-c-struct struct (list int '*)))
                     (* 10 (sizeof int)))

=> shutdown guile!

with  my test C function..

typedef struct {
  int a;
  int b;
  int c[2000];
} Foo;

Foo make_foo(int a, int b) {
  Foo foo = {.a = a, .b = b};
  return foo;
}

((pointer->procedure
   (list int int '*)
   (dynamic-func "make_foo" libfoo)
   (list int int))
 10 10)

shutdown…. I also test in SBCL(cffi-libffi)
(cffi:defcstruct foo
  (a :int)
  (b :int)
  (c :int :count 2000))

(cffi:defcfun "make_foo" (:struct foo)
  (a :int)
  (b :int))

(make-foo 10 20)  => (C #.(SB-SYS:INT-SAP #X0CC6C0A8) B 20 A 10)

but when I change to 
(cffi:defcstruct foo
  (a :int)
  (b :int)
  (c :pointer))

when call (make-foo 10 20), then shut down.
but It seems consequent, array and pointer are different type.


> On Mar 30, 2016, at 6:03 PM, Taylan Ulrich Bayırlı/Kammer <address@hidden> 
> wrote:
> 
> <address@hidden> writes:
> 
>> On Wed, Mar 30, 2016 at 10:03:28AM +0200, Taylan Ulrich Bayırlı/Kammer wrote:
>>> Park SungMin <address@hidden> writes:
>>> 
>>>> (let ((c-type (list int int (make-list 20000 int))))
>>>>    (parse-c-struct
>>>>     ((pointer->procedure
>>>>       c-type
>>>>       (dynamic-func "make_foo" libfoo)
>>>>       (list int int))
>>>>      4 11)
>>>>     c-type))
>>>> 
>>>> also run well…but seems less effective.(if more bigger size…2000000??) 
>>> 
>>> You could create the type object once at program startup and use it
>>> many times.
>>> 
>>>    (define foo-type
>>>      (list int int (make-list 2000000 int)))
>> 
>> If I understood Park SungMin right, the problem is rather with the
>> representation of a huge array as a list?
> 
> Oh I see.
> 
> For me, the following works:
> 
>    (define type (list int (make-list 10 int)))
> 
>    (define struct (make-c-struct type (list 42 (make-list 10 42))))
> 
>    (parse-c-struct struct (list int '*))
>      => (1 #<pointer 0x200000002>) 
> 
> Is it different when the struct really comes from the C library?
> 
> Taylan
>