libusb_hotplug_register_callback不接受我的回调函数

Question

我正在用visual studio 2012开发一个应用程序来检测vc++中USB的插入和拔出情况。我已经添加了libusb 1.0库，它现在是一个跨平台库。

当我尝试注册事件处理程序时，我遇到了回调函数的编译问题。

#include "detect_usb_libusb.h"
#include <QtWidgets/QApplication>
#include <time.h>
#include <stdio.h>
#include <libusb.h>


static int count = 0;    

int hotplug_callback(struct libusb_context *ctx, struct libusb_device *dev,
                                                libusb_hotplug_event event, void *user_data) {
        static libusb_device_handle *handle = NULL;
        struct libusb_device_descriptor desc;
        int rc;
        (void)libusb_get_device_descriptor(dev, &desc);
        if (LIBUSB_HOTPLUG_EVENT_DEVICE_ARRIVED == event) {
            rc = libusb_open(dev, &handle);
            if (LIBUSB_SUCCESS != rc) {
                printf("Could not open USB device\n");
            }
        } else if (LIBUSB_HOTPLUG_EVENT_DEVICE_LEFT == event) {
            if (handle) {
                libusb_close(handle);
                handle = NULL;
            }
        } else {
                printf("Unhandled event %d\n", event);
        }
        count++;
  return 0;
}

int main (void) {
  libusb_hotplug_callback_handle handle;
  int rc;
  libusb_init(NULL);

  rc = libusb_hotplug_register_callback(  NULL, (libusb_hotplug_event) (LIBUSB_HOTPLUG_EVENT_DEVICE_ARRIVED |
                                            LIBUSB_HOTPLUG_EVENT_DEVICE_LEFT), LIBUSB_HOTPLUG_ENUMERATE,
                                            0x2047, LIBUSB_HOTPLUG_MATCH_ANY,
                                            LIBUSB_HOTPLUG_MATCH_ANY, hotplug_callback, NULL,
                                            &handle);  

  if (LIBUSB_SUCCESS != rc) {
    printf("Error creating a hotplug callback\n");
    libusb_exit(NULL);
    return EXIT_FAILURE;
  }
  while (count < 2) {
    _sleep(10000);
  }
  libusb_hotplug_deregister_callback(NULL, handle);
  libusb_exit(NULL);
  return 0;
}

我从libusb API获得了这段代码，现在我真的搞不懂了。异常是这样的：

 error C2664: 'libusb_hotplug_register_callback' : cannot convert parameter 7 from 'int (__cdecl *)(libusb_context *,libusb_device *,libusb_hotplug_event,void *)' to 'libusb_hotplug_callback_fn'

但我不知道如何将"int ( __cdecl *)“函数转换为"int (* libusb_hotplug_callback_fn)”

非常感谢

Answer 1

是这样的：static int LIBUSB_CALL hotplug_callback(libusb_context *ctx, libusb_device *dev, libusb_hotplug_event event, void *user_data)来源：https://github.com/libusb/libusb/blob/master/examples/hotplugtest.c

Answer 2

我在VS 2013上也遇到了同样的错误，在libusb_hotplug_register_callback()中只需更改

hotplug_callback

至

(libusb_hotplug_callback_fn) hotplug_callback

Answer 3

这很可能是由于

 rc = libusb_hotplug_register_callback(  NULL, (libusb_hotplug_event) (**LIBUSB_HOTPLUG_EVENT_DEVICE_ARRIVED |LIBUSB_HOTPLUG_EVENT_DEVICE_LEFT**), LIBUSB_HOTPLUG_ENUMERATE,0x2047, LIBUSB_HOTPLUG_MATCH_ANY,                                LIBUSB_HOTPLUG_MATCH_ANY, hotplug_callback, NULL,&handle); 

尝试使用

rc = libusb_hotplug_register_callback(  NULL, (libusb_hotplug_event) (LIBUSB_HOTPLUG_EVENT_DEVICE_ARRIVED), LIBUSB_HOTPLUG_ENUMERATE,0x2047, LIBUSB_HOTPLUG_MATCH_ANY,                                LIBUSB_HOTPLUG_MATCH_ANY, hotplug_callback, NULL,&handle);

这是因为由于or (|)运算符，它在逐位OR运算后转换为整数。