Alex
You should have a look at this article by Martin Neitzel
http://juggle.gaertner.de/bnp/c2j.html
from Vol 16-2 of Vector published by the BAA ( https://vector.org.uk/ )
in October 1999.
The article is old, so be on your guard as regards language changes.
Is it still valid? I think so. I hope others can comment.
~ Gilles
Le 2021-10-05 à 13:45, Eric Iverson a écrit :
Your question, and future discussion, is more appropriate to the
programming forum.
This is a messy area and alignment and compiler differences are a
complication.
Here is some handwaving. Let the forum know if you need more.
tohex =: [: ,"2 ' ' (,"1) '0123456789ABCDEF' {~ 16 16 #: a. i. ]
d=. 2.3 2.4
_2{.3!:3 d
i=. 23
_1{.3!:3 i
s=. (2 fc d),2 ic i
tohex s
66 66 66 66 66 66 02 40 33 33 33 33 33 33 03 40 17 00 00 00
NB. s has the bit pattern you want
NB. call your routine as: ('.... n *c' cd s NB. no result, pointer to char
data that is your struct data
On Tue, Oct 5, 2021 at 1:36 PM Raul Miller <[email protected]> wrote:
C structs are a bit tricky because different compilers, and different
compiler options, can result in different layouts in memory for the
structs.
That said, something like this looks like it should be straightforward
(I expect that most compilers would not introduce padding between
members of the struct).
FYI,
--
Raul
On Tue, Oct 5, 2021 at 1:33 PM 'robert therriault' via General
<[email protected]> wrote:
Alex,
I haven't done very much of that myself, but have you looked at chapter
21 of JforC?
https://www.jsoftware.com/help/jforc/calling_external_programs.htm#_Toc191734429
Cheers, bob
On Oct 5, 2021, at 09:21, Alex Shroyer <[email protected]> wrote:
How do I send/receive data structures to/from C functions using the cd
verb?
For example if I have this C library saved as /tmp/example.dylib, how
do I
call it from J?
// C code:
struct stuff {double a[2]; int i;};
void fn(struct stuff *x) {x->a[x->i] += 100;}
NB. J code:
data =: (2.3 4.5);0 NB. the data I would like to send to fn (array
of 2
doubles; int)
'/tmp/example.dylib fn (declaration)' cd (parameters)
Specifically, what do I use for the (declaration) and what do I use for
(parameters)?
I presume I should use something from
https://www.jsoftware.com/help/dictionary/dx003.htm but I'm unsure
how to
then specify it in the (declaration).
Is there a relevant example somewhere?
Thanks,
Alex
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