[英]libusb callback_in function as a member of a class in C++
当在C ++中作为类的成员调用时,我在libusb_fill_bulk_transfer
定义和使用回调函数时libusb_fill_bulk_transfer
问题。
这是类中的定义:
namespace usb_connector
{
class USBConnector
{
public:
USBConnector();
~USBConnector();
int connect(void);
void read(void);
void write(unsigned char *);
void disconnect(void);
void LIBUSB_CALL callback_in(struct libusb_transfer*);
...
这是类中的实现:
void LIBUSB_CALL usb_connector::USBConnector::callback_in(struct libusb_transfer *transfer)
{
if (transfer == NULL) {
cout << "No libusb_transfer..." << endl;
}
else {
cout << "libusb_transfer structure: " << endl;
cout << "actual_length = " << transfer->actual_length << endl;
for (int i = 0; i < transfer->actual_length; i++) {
cout << transfer->buffer[i];
}
cout << endl;
}
return;
}
以下是我称之为:
...
...
libusb_fill_bulk_transfer( transfer_in, usb_dev, USB_ENDPOINT_IN,
in_buffer, LEN_IN_BUFFER, callback_in, NULL, 0);
...
...
我得到的错误如下:
错误:无法将'usb_connector :: USBConnector :: callback_in'从类型'void(usb_connector :: USBConnector ::)(libusb_transfer *)'转换为'libusb_transfer_cb_fn {aka void( )(libusb_transfer )}'in_buffer,LEN_IN_BUFFER,callback_in, NULL,0);
如何将回调函数作为类的成员以及如何调用它?
指向类成员函数的指针和指向函数的指针在C ++中是不兼容的。
根据文档,回调的原型是:
typedef void( * libusb_transfer_cb_fn) (struct libusb_transfer *transfer)
而struct libusb_transfer
有user_data
字段,显然在你设置回调期间填写,所以你需要一个包装器:
void LIBUSB_CALL callback_wrapper(struct libusb_transfer *transfer)
{
usb_connector::USBConnector *connector = reinterpret_cast<usb_connector::USBConnector*>(transfer->user_data);
connector->callback_in(transfer);
}
并通过this
通话过程中:
...
...
libusb_fill_bulk_transfer( transfer_in, usb_dev, USB_ENDPOINT_IN,
in_buffer, LEN_IN_BUFFER, callback_wrapper, this, 0);
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