Re: [cffi-devel] C to Lisp
your Hell-function has return value void so there is no return (apart
from that return 0 that should not be there), hence the NIL. Printf
prints to stdout so maybe you just didn't see it?
On 27.11.2013 17:41, Greg Bennett wrote:
Good morning,
I (think I) might be close to getting a result in having a C function
return its output to Lisp. I shall be very grateful for comments and
corrections to what I have done, and thank readers for their patience.
Here is the C-function from which I wish to get the result Hello Lisp
from C on the lisp side:
/* Hello.c program */
#includestdio.h
void Hello(void)
{
printf(Hello Lisp from C\n);
return 0 ;
}
At the end of the process, I hope to be able to do this on the Lisp
side:
(defcfun (Hello HiFromC) (:void))
and then
(HiFromC) - Hello Lisp from C
Both C and Lisp sessions are below in case details are relevant.
Somewhere I have missed a critical element.
Thanks to a message from Luis Oliveira pointing me to the necessity of
using a shared library as the intermediary between C and Lisp. There
seem to be as many recipes for creating such libraries as there are
posters of the topic, and as many variations on the code too. I have
put together the C side following very much this page:
www.cprogramming.com/tutorial/shared-libraries-linux-gcc.html
In file /home/gwbennett/Hello.h
#ifndef Hello_h__
#define Hello_h__
extern void Hello(void);
#endif // Hello_h__
In file /home/gwbennett/Hello.c
/* Hello program */
#includestdio.h
void Hello(void)
{
printf(Hello Lisp from C\n);
return 0 ;
}
In file main.c
/* This is main.c to go with Hello.c,h */
#include stdio.h
#include Hello.h
int main (void)
{
Hello();
return 0;
}
Then
gcc -c -Wall -Werror -fpic Hello.c - OK
gcc -shared -o libfHello.so Hello.o - OK
gcc -L/home/gwbennett -Wall -o test main.c -lHello - OK
Step 4 of the above page is about making the library visible.
I have tried all 3 routes with the same results; at the moment I have
taken the path of installing libHello.so in /usr/lib (and
in /usr/loca/lib too)as described in the Section Using ldconfig to
modify ld.so
gcc -Wall -o test main.c -lfoo - OK
ldd test | grep foo - /usr/locl/lib/libHello.so (0x7f946c0c4000)
./test - Hello Lisp from C
so things seem to work down the C-side
On the Lisp side I (hope I) am following the cffi manual page 10. I
assume that cffi looks for shared libraries in the same sort of 'system'
places as C, but just in case, see page 106 on
*foreign-library-directories*.
Start ccl version 1.9-r15972M (LinuxX8664)
(require :cffi) - OK
(defpackage :cffi-user
(:use :common-lisp :cffi)) - OK
(in-package :cffi-user) - OK
;P106
(pushnew #P/usr/lib *foreign-library-directories* :test #'equal) - OK
(pushnew #P/usr/local/lib *foreign-library-directories* :test #'equal)
- OK
(load-foreign-library '(:default LibHello)) - OK
;; I think I should be able to define the C - Lisp name function
(defcfun (Hello HiFromC) (:void)) - HIFROMC
;; and execute it to get the message
(HiFromC) - NIL
;; .. so evidently I have not completely understood what is necessary to
achieve the desired result.
Again, thanks for any and all assistance.
Cheers /Greg Bennett
Re: [cffi-devel] C to Lisp
Greg Bennett gwbenn...@sentex.ca writes:
Good morning,
I (think I) might be close to getting a result in having a C function
return its output to Lisp. I shall be very grateful for comments and
corrections to what I have done, and thank readers for their patience.
Here is the C-function from which I wish to get the result Hello Lisp
from C on the lisp side:
/* Hello.c program */
#includestdio.h
void Hello(void)
{
printf(Hello Lisp from C\n);
return 0 ;
}
At the end of the process, I hope to be able to do this on the Lisp
side:
(defcfun (Hello HiFromC) (:void))
and then
(HiFromC) - Hello Lisp from C
Both C and Lisp sessions are below in case details are relevant.
Somewhere I have missed a critical element.
Thanks to a message from Luis Oliveira pointing me to the necessity of
using a shared library as the intermediary between C and Lisp. There
seem to be as many recipes for creating such libraries as there are
posters of the topic, and as many variations on the code too. I have
put together the C side following very much this page:
www.cprogramming.com/tutorial/shared-libraries-linux-gcc.html
In file /home/gwbennett/Hello.h
#ifndef Hello_h__
#define Hello_h__
extern void Hello(void);
#endif // Hello_h__
In file /home/gwbennett/Hello.c
/* Hello program */
#includestdio.h
void Hello(void)
{
printf(Hello Lisp from C\n);
return 0 ;
}
In file main.c
/* This is main.c to go with Hello.c,h */
#include stdio.h
#include Hello.h
int main (void)
{
Hello();
return 0;
}
Then
gcc -c -Wall -Werror -fpic Hello.c - OK
gcc -shared -o libfHello.so Hello.o - OK
gcc -L/home/gwbennett -Wall -o test main.c -lHello - OK
Step 4 of the above page is about making the library visible.
I have tried all 3 routes with the same results; at the moment I have
taken the path of installing libHello.so in /usr/lib (and
in /usr/loca/lib too)as described in the Section Using ldconfig to
modify ld.so
gcc -Wall -o test main.c -lfoo - OK
ldd test | grep foo - /usr/locl/lib/libHello.so (0x7f946c0c4000)
./test - Hello Lisp from C
so things seem to work down the C-side
On the Lisp side I (hope I) am following the cffi manual page 10. I
assume that cffi looks for shared libraries in the same sort of 'system'
places as C, but just in case, see page 106 on
*foreign-library-directories*.
Start ccl version 1.9-r15972M (LinuxX8664)
(require :cffi) - OK
(defpackage :cffi-user
(:use :common-lisp :cffi)) - OK
(in-package :cffi-user) - OK
;P106
(pushnew #P/usr/lib *foreign-library-directories* :test #'equal) - OK
(pushnew #P/usr/local/lib *foreign-library-directories* :test #'equal)
- OK
(load-foreign-library '(:default LibHello)) - OK
;; I think I should be able to define the C - Lisp name function
(defcfun (Hello HiFromC) (:void)) - HIFROMC
;; and execute it to get the message
(HiFromC) - NIL
;; .. so evidently I have not completely understood what is necessary to
achieve the desired result.
Are you aware of the difference between printing to the standard output
and returning a result?
And all you have to do is:
#include stdio.h
void hello () {
printf(Hello Lisp from C\n);
}
gcc foo.c -fPIC -o foo.so
? (cffi:load-foreign-library /tmp/foo.so)
#FOREIGN-LIBRARY FOO.SO-6780 foo.so
? (cffi:foreign-funcall hello)
Hello Lisp from C
NIL
?
If you still don't see any output,
just add fflush(stdout);
--
With best regards, Stas.
