问题
native c header:
typedef HANDLE HCAMERA;
int Begin(HCAMERA* h);
int End(HCAMERA h);
HANDLE is defined:
typedef void *HANDLE;
native c source I want:
HCAMERA h;
int r = 0;
r = Begin(&h);
VERIFY(r);
r = End(h);
VERIFY(r);
I tried following code in sbcl 1.3.1 but not working.
(cffi:use-foreign-library "camera.dll")
(cffi:defcfun "Begin" :int
(handle :pointer))
(cffi:defcfun "End" :int
(handle :pointer))
(defparameter *camera* (cffi:foreign-alloc :pointer)) ; alloc handle
(cffi:with-foreign-object (handle :pointer)
(setf (cffi:mem-ref handle :pointer) *camera*) ; handle address
(Begin handle)
(End *camera*))
BTW: HOW TO GET THE ADDRESS OF THE FOREIGN OBJECT (camera)? AM I DOING IT RIGHT?
回答1:
You can get the address like this:
(defun get-foreign-address (obj)
(write-to-string (cffi:pointer-address obj) :base 16))
If you have this C file
#include <stdio.h>
typedef void *HANDLE;
typedef HANDLE HCAMERA;
int Begin(HCAMERA* h);
int End(HCAMERA h);
int Begin(HCAMERA* h) {
printf("Address from Begin: %p\n", h);
return 0;
};
int End(HCAMERA h) {
printf("Address from End: %p\n", (void*)&h);
return 0;
};
you can see, e.g. by this common lisp file, that you get the same address from lisp and C for handle
. It isn't the same for *camera*
because it is passed by value. I tried it on Linux, but I think it should be the same on Windows, just change camera.so
to camera.dll
.
(cffi:use-foreign-library "camera.so")
(cffi:defcfun "Begin" :int
(handle :pointer))
(cffi:defcfun "End" :int
(handle :pointer))
(cffi:defcvar ("stdout" stdout) :pointer)
(defparameter *camera* (cffi:foreign-alloc :pointer))
(cffi:with-foreign-object (handle :pointer)
(format t "Address from Lisp: ~a~%" (get-foreign-address handle))
(Begin handle)
(format t "Address from Lisp: ~a~%" (get-foreign-address *camera*))
(End *camera*))
(cffi:foreign-funcall "fflush" :pointer stdout :int)
Possible pitfall: If I use this lisp code from Emacs, I don't see the stdout from C. I executed it from the command line with sbcl --script file.lisp
. Hope, that helps you somehow.
回答2:
I finally figured out using following code:
(defparameter *camera-handle* (cffi:null-pointer))
(defun camera-open ()
(unless (cffi:null-pointer-p *camera-handle*)
(EndHVDevice (cffi:mem-ref *camera-handle* :pointer))
(cffi:foreign-free *camera-handle*))
(setf *camera-handle* (cffi:foreign-alloc :pointer))
(BeginHVDevice *camera-handle*))
(defun camera-close ()
(unless (cffi:null-pointer-p *camera-handle*)
(EndHVDevice (cffi:mem-ref *camera-handle* :pointer))
(cffi:foreign-free *camera-handle*)
(setf *camera-handle* (cffi:null-pointer))))
来源:https://stackoverflow.com/questions/34646657/how-to-call-native-c-function-with-windows-handle-in-common-lisp-cffi