如何在常见的Lisp/cffi中使用Windows HANDLE调用本机C函数 [英] How to call native c function with windows HANDLE in common lisp / cffi

问题描述

本地c标头:

typedef HANDLE HCAMERA;
int Begin(HCAMERA* h);
int End(HCAMERA h);

HANDLE已定义:

HANDLE is defined:

typedef void *HANDLE;

我想要的本地c源:

HCAMERA h;
int r = 0;
r = Begin(&h);
VERIFY(r);
r = End(h);
VERIFY(r);

我尝试了sbcl 1.3.1中的以下代码，但无法正常工作.

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*))

顺便说一句:如何获得外国对象(相机)的地址?我做对了吗?

BTW: HOW TO GET THE ADDRESS OF THE FOREIGN OBJECT (camera)? AM I DOING IT RIGHT?

推荐答案

您可以这样获得地址:

(defun get-foreign-address (obj)
  (write-to-string (cffi:pointer-address obj) :base 16))

如果您有此C文件

#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;
};

例如，您可以看到通过这个通用的Lisp文件，您从Lisp和C中获得了与handle相同的地址.对于*camera*，它是不同的，因为它是按值传递的.我在Linux上尝试过，但是我认为在Windows上应该是相同的，只需将camera.so更改为camera.dll.

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)

可能的陷阱:如果我使用Emacs的lisp代码，则看不到C语言的标准输出.我使用sbcl --script file.lisp从命令行执行了它.希望能以某种方式对您有所帮助.

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.

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