On 4/20/21 4:36 PM, Vladimir Zhbanov wrote:
Hi Matt,
On Tue, Apr 20, 2021 at 06:46:27AM -0700, Matt Wette wrote:
On 4/20/21 5:47 AM, Matt Wette wrote:
On 4/20/21 2:29 AM, Vladimir Zhbanov wrote:
Hi Guile users and devs,
I'm the current maintainer of Lepton EDA suite, an about five year
old fork of geda-gaf with accent to moving more functionality to
Scheme code. I'm not sure if it is acceptable to advertise it
here, please let me know if not. I just know several Guix
packagers are reading this mailing list and would like to announce
a new version of Lepton, 1.9.14 has been released on April, 7:
https://github.com/lepton-eda/lepton-eda/releases/tag/1.9.14-20210407
Sweet. Thanks for posting this. I will take a look at your problem.
It'll require digging into the eda_..._dirs function.
The following should work as a complete program on a system w/ glib.
You need to first convert the result to a bytevector and then access the
elements (pointers) one at a time. Note that we don't know how big the
array returned from the C function is. I pick an oversized value of 100.
(use-modules (system foreign))
(use-modules (rnrs bytevectors))
(define glib (dynamic-link "libglib-2.0"))
(define g-get-system-data-dirs
(let ((f (pointer->procedure
'* (dynamic-func "g_get_system_data_dirs" glib) (list)))
(bv-pointer-ref (cond
((= (sizeof '*) 8) bytevector-u64-native-ref )
((= (sizeof '*) 4) bytevector-u32-native-ref )
(else (error "hmmm"))))
(BIG 100))
(lambda ()
(let* ((r (f))
(p (pointer->bytevector r (* BIG (sizeof '*)))))
(let loop ((ix 0))
(let* ((ad (bv-pointer-ref p ix))
(sp (make-pointer ad)))
(if (equal? %null-pointer sp)
'()
(cons (pointer->string sp) (loop (+ ix (sizeof '*)))))))))))
(simple-format #t "~S" (g-get-system-data-dirs))
Thank you for your replies!
Probably, I missed something here, so I'll try to elaborate a bit
on my initial question. The function eda_get_system_data_dirs()
mentioned in my first message has the same type, is defined the
same way using dynamic-func though in liblepton instead of glib,
and works on mostly the same array as glib's
g_get_system_data_dirs(). The function I've shown works well and
outputs the same results as yours. It simply uses a bit more
upper level interface, IIUC. So the first question is: I wonder,
if using bytevectors directly adds something here?
Another issue is a little more confusing for me. I read in
several places that even on the same system different compilators,
say gcc and g++, may use different alignment even for basic C
types like, say, double. What will they do on different platforms
then? May it be that (alignof '*) will be twice greater than
(sizeof '*)? In such a case using multiplied sizeof of pointer
for searching the location of a pointer in memory would be just
dangerous. I used sizeof in the first version of my code but
started to doubt if it is correct and how portable it is.
Thanks,
Vladimir
Hey. I used the glib routine because it returns the same form,
if I read correctly. The return value is a pointer to a sequence
of (C) pointers. On my machine they are 8 bytes each. So, if
the function is returning three strings, say, the first 8 bytes will
be a pointer to the first string and last 8 bytes (of a total of 32
= 4 * 8) will be zero. You need to access the three 8-byte
pointer values as numbers and convert to guile pointers to
access the strings. I don't see a way around that.
I don't see this being a problem with gcc vs g++. Maybe in
structs with mixed types, but not here, IMO.
Matt
