I made the member function static and prototype needed to be modified:
static void LIBUSB_CALL readDataFromBuffer(struct libusb_transfer *);
سؤال
I am using libusb to interact with a usb device. I have created a Class and a member function will receive the input from the device and process it. I am using Asynchronous api. Now the libusb_fill_bulk_transfer() function call throws a compilation error:
void MyDeviceClass::on_connectButton_clicked()
{
int r; //for return values
ssize_t cnt; //holding number of devices in list
r = libusb_init(&ctx); //initialize the library for the session we just declared
if(r < 0) {
qDebug()<<"Init Error "<<r<<endl; //there was an error
return;
}
...
...
...
libusb_fill_bulk_transfer( transfer_in, dev_handle, USB_ENDPOINT_IN,
inBuffer, LEN_IN_BUFFER,readDataFromBuffer,NULL,0);
libusb_submit_transfer(transfer_in);
QtConcurrent::run (this,&MyDeviceClass::eventThread);
}
The compiler suggests using &MyDeviceClass::readDataFromBuffer as a function pointer but that still throws an error. I tried using static members, and even static non-member functions but all in vain. Please help me in passing the callback to this function. I am using Qt, and probably won't like to use boost libraries. Please note that libusb_fill_bulk_transfer(...) is invoked inside a member function of MyDeviceClass.
المحلول
I made the member function static and prototype needed to be modified:
static void LIBUSB_CALL readDataFromBuffer(struct libusb_transfer *);
نصائح أخرى
what is the compile error when you use a non member function?
Edit: this should be LIBUSB_CALL:
void LIBUSB_CALL BulkTransferCallback(struct libusb_transfer *transfer) {
// This assumes that you set transfer::user_data to be a pointer to
// an instance of the MyDeviceClass class.
MyDeviceClass* mdc = reinterpret_cast<MyDeviceClass*>(transfer->user_data);
mdc->onBulkTransferCallback(transfer);
}
Then when you set the pointer, use:
transfer.callback = &BulkTransferCallback;
As you answered yourself, actually it should be __stdcall which is defined by LIBUSB_CALL. Their documentation should include this in the function pointer typedef to remove the ambiguity.
The lib_usb api defines the function libusb_fill_bulk_transfer with:
static void libusb_fill_bulk_transfer (struct libusb_transfer *transfer, libusb_device_handle *dev_handle, unsigned char endpoint, unsigned char *buffer, int length, libusb_transfer_cb_fn callback, void *user_data, unsigned int timeout)
It is possible to add a static class function to your class and call the non-static member-function of the class within this static function.
You this Object would be at the place of void *user_data.
In the static class function you would have to cast the member of transfer->user_data correctly to your class.