Chapter 8. Basic Examples

    	struct usb_bus *busses;
    
    	usb_init();
    	usb_find_busses();
    	usb_find_devices();
    
    	busses = usb_get_busses();
        

    	struct usb_bus *bus;
    	int c, i, a;
    
    	/* ... */
    
    	for (bus = busses; bus; bus = bus->next) {
    		struct usb_device *dev;
    
    		for (dev = bus->devices; dev; dev = dev->next) {
    			/* Check if this device is a printer */
    			if (dev->descriptor.bDeviceClass == 7) {
    				/* Open the device, claim the interface and do your processing */
    				...
    			}
    
    			/* Loop through all of the configurations */
    			for (c = 0; c < dev->descriptor.bNumConfigurations; c++) {
    				/* Loop through all of the interfaces */
    				for (i = 0; i < dev->config[c].bNumInterfaces; i++) {
    					/* Loop through all of the alternate settings */
    					for (a = 0; a < dev->config[c].interface[i].num_altsetting; a++) {
    						/* Check if this interface is a printer */
    						if (dev->config[c].interface[i].altsetting[a].bInterfaceClass == 7) {
    							/* Open the device, set the alternate setting, claim the interface and do your processing */
    							...
    						}
    					}
    				}
    			}
    		}
    	}