Problem getting libusb datarecieved event to send signal

[high_flyer]

what is the protype of libusb_fill_interrupt_transfer()?
Usually call back set functions take also a 'user param' to allow access to a user class.
What is the 'NULL' parameter?

[sisco]

what is the protype of libusb_fill_interrupt_transfer()?
Usually call back set functions take also a 'user param' to allow access to a user class.
What is the 'NULL' parameter?

from libusb documentation:

static void libusb_fill_interrupt_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	 
	) 			[inline, static]
 
Helper function to populate the required libusb_transfer fields for an interrupt transfer.
 
Parameters:
    	transfer 	the transfer to populate
    	dev_handle 	handle of the device that will handle the transfer
    	endpoint 	address of the endpoint where this transfer will be sent
    	buffer 	data buffer
    	length 	length of data buffer
    	callback 	callback function to be invoked on transfer completion
    	user_data 	user data to pass to callback function
    	timeout 	timeout for the transfer in milliseconds

static void libusb_fill_interrupt_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	 
	) 			[inline, static]

Helper function to populate the required libusb_transfer fields for an interrupt transfer.

Parameters:
    	transfer 	the transfer to populate
    	dev_handle 	handle of the device that will handle the transfer
    	endpoint 	address of the endpoint where this transfer will be sent
    	buffer 	data buffer
    	length 	length of data buffer
    	callback 	callback function to be invoked on transfer completion
    	user_data 	user data to pass to callback function
    	timeout 	timeout for the transfer in milliseconds

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the NULL parameter is the user_data param i thougnt since i didnt have anything i wanted to send with it i just used NULL.